Structural and biological aspects of Z-DNA: The function
of the vaccinia virus Z-DNA-binding protein E3L
Molly Spore
Senior Comprehensive Paper
The Catholic University of America
Spring 2007
Spore 2.
Abstract
Crystal structural features along with biological aspects of Z-DNA were examined in order to
evaluate the biochemical relevance to alternative DNA structures. Z-DNA binding proteins are
activated to inhibit apoptosis, programmed cell death, when bound to Z-DNA. Z-DNA binding
proteins also provide stability for the DNA molecule. The Z-DNA-binding activity of the Nterminal domain of the viral protein E3L is necessary for viral pathenogenesis. E3L, the vaccinia
virus protein, is crucial for virulence and anti-apoptotic activity. The Z-DNA-binding domain of the
E3L protein in HeLa cells is found to localize itself within the nucleus of the vaccinia virus. HeLa
cells are an immortal cell line used in medical research, which were derived from cervical cancer
cells. The N-terminus of Z-DNA-binding proteins, such as E3L, stabilizes the Z-DNA in the
promoter region, which may result in transactivation of the gene. HeLa cells depend on E3L to
inhibit the hygromyocin B (antibiotic essential to the growth arrest of a cell in response to toxins)induced apoptosis, and Z-DNA binding of E3L is essential for this inhibition effect. Z-DNA
binding domains in other proteins are also effective in blocking apoptosis. Thus, Z-DNA plays an
important role in vaccinia virus pathenogenesis. An open question is the occurrence of Z-DNA in
stabilizing similar proteins in other species.
Spore 3.
Introduction
The discovery of the DNA structure in 1953 by Watson and Crick led to research of the function of
the DNA molecule in order to understand its role in the inheritance of genes.1 The features of the
DNA molecule that were discovered by Watson and Crick were two polynucleotide chains that run
in opposite directions from one another, coiling around an axis to form a double helix. The
deoxyribose sugar and phosphate units are on the outside of the helix. The inside of the helix
consists of purine and pyrimidine bases. The bases are adenine, thymine, guanine, and cytosine;
adenine always pairs with thymine and guanine always pairs with cytosine. The A-T bases are held
together by two hydrogen bonds whereas the G-C bases are held together by three hydrogen bonds.2
DNA Secondary Structures
Beside the common structural features that were revealed by Watson and Crick in 1953, other
secondary structures or varieties of DNA were discovered. Watson and Crick identified the B-DNA
form, but a similar A-DNA was also found to exist in dehydrated environments.2 A and B-DNA are
both right-handed helices with Watson and Crick base pairings. DNA varieties are differentiated
from each other by three structural features: glycosidic bonds, major and minor grooves, and sugar
ring puckerings.
A. Glycosidic Bonds
A great factor in the DNA structure is the glycosidic bond. A glycosidic bond is the linkage between
the N-9 of a purine or the N-1 of a pyrimidine with the C-1 of a deoxyribose sugar.2 For pyrimidines
in the syn conformation, the oxygen substituent at position C-2 lies immediately above the furanose
ring; in the anti conformation, this steric interference is avoided. Consequently, pyrimidine
nucleosides favor the anti conformation. Purine nucleosides can adopt either the syn or anti
Spore 4.
conformation. In either conformation, the roughly planar furanose and base rings are not coplanar
but lie at approximately right angles to one another.2 Refer to Figure 1 to examine the differences
between syn and anti-glycosidic angles of guanosine and the dependence upon the position of the
structures to determine its stability. This steric avoidance occurs in the same way for the glycosidic
bonds of cytosine.
Figure 1. Rotation around the glycosidic bond is sterically hindered; syn versus anti
conformations in nucleosides are shown.2
B. Major and Minor Grooves
DNA has major and minor grooves in their helical structures. The grooves are a result of the
glycosidic bonds of a base pair not being exactly opposite from one another. As shown in Figure 2,
the minor groove of DNA consists of pyrimidine O-2 and purine N-3 of the base pair. The major
groove is on the opposite side of this base pair, which contains the methyl group of thymine.
The major groove in B-DNA is 12 Å wide and 8.5 Å deep, which is wider and deeper than the
minor groove, which is 6 Å wide and 7.5 Å deep. The wider groove in B-DNA makes this form
more accessible to interaction with other molecules and proteins.3 Therefore, the A-DNA helix is
wider and shorter than the B helix, and its base pairs are tilted rather than perpendicular to the helix
Spore 5.
as in B-DNA. The reason for A-DNA’s stability in dehydrated environments is that phosphate and
other groups within A-DNA bind fewer H20 molecules than in B-DNA.2
Figure 2. Because of the glycosidic bonds of a DNA helix not being exactly opposite
to one another, each base pair consists of a larger side that is known as the major
groove and a smaller side known as a minor groove.2
C. Sugar Ring Puckering
The different conformations of A and B-DNA are mostly due to puckerings in the deoxyribose
sugar units. In A-DNA, the ring of the ribose has the C3'-endo configuration, with the carbon 3
raised above the plane of the sugar ring, while carbon 2 is below the plane. In B-DNA, the ring is in
the C2'-endo configuration, with the C2 atom above the sugar plane and the C3 atom below it. The
C-3’ lies out of the plane that is formed by the deoxyribose furanose ring in A-DNA, accounting for
an 11 degree tilting of the base pairs from the helix. In contrast, the C-2’ of B-DNA’s deoxyribose
sugars lie out of the plane, formed by the other four atoms of the ribose ring.
B-DNA has more phosphates exposed to hydration by H20 molecules and thus making the B-DNA
form the most common in all cells.2 As shown in Figure 3, the base pairs of DNA are not perfectly
coplanar, with angles differing among the DNA varieties. The bases are twisted with respect to one
another, depending on the base sequences. The extent of the twisting gives rise to variations among
Spore 6.
the DNA secondary structures. It is hypothesized that proteins searching for specific sequences in a
DNA molecule can recognize the sequence by the specific shape of the double helix.2
Figure 3. The bases of a DNA molecule are not perfectly coplanar, which
form the specific arrangement of the DNA double helix.2
Z-DNA: Structural Features
Although the information gained from A and B-DNA was vast, the discovery of DNA secondary
structures was not yet complete. With the help of Dutch chemist Jacques Van Boom who
synthesized oligomers and Andy Wang who was responsible for crystallizing the structure,
Alexander Rich from MIT at Cambridge, MA discovered the first crystal structure of a new variety
of DNA, termed as the Z-DNA molecule.3 This first Z-oligonucleotide duplex single structure to be
solved was discovered in 1979, consisting of an alternating pyrimidine-purine sequence
d(CGCGCG)2. It was not until the late 1970’s that x-ray diffraction studies could be performed to
prove the structure of Z-DNA.3
Spore 7.
Z-DNA structural features consist of the purine, deoxyguanosine and deoxyadenine, nucleosides
having alternating syn-anti glycosidic angles. These glycosidic angles range from 55 to 80 degrees (a
mean of 60 degrees). The pyrimidine, deoxycytidine and deoxythymidine, nucleosides have antiglycosidic angles ranging from -145 to -160 degrees (a mean of -152 degrees). These glycosidic bond
features are the same as glycosidic bond features of A and B DNA. Although A-T base pairings can
exist within the Z-DNA helix, A-T base pairings destabilize the Z-DNA helix.3 A-T base pairings
exhibit Z-DNA phobicity because the free energy cost of changing a C-G base pair to an A-T base
pair in Z-DNA is very high, where the free energy cost of changing a C-G base pair to A-T base pair
in A and B DNA is 2 kcal/mol lower than in Z-DNA.4 If A-T base pairings are present within the
Z-DNA molecule, the cytosines must be 5-methlyated for the poly-CGATCG sequence to be
stabilized. The C-G and A-T base pairs in Z-DNA are of standard Watson and Crick type.3
The Z-DNA structure was determined at a resolution of 0.9 Å.3 It revealed surprising characteristics
of a left-handed double helix held together by Watson and Crick base pairs, in contrast to the A and
B-DNA that are right-handed helices. Because of the consequences that base sequences can have on
the conformation of the helix as shown in Figure 3, every other base of the d(CGCGCG)2 sequence
rotates around glycosidic bonds so that the bases alternate in anti and syn conformations along the
chain. So although the glycosidic bonds in Z-DNA adopt the same conformations as A and BDNA, the torsion angles in Z-DNA are different from A and B-DNA; the dC-dG and dG-dC
phosphodiester linkages adopt different conformations because of torsional strain. This results in a
zig-zag arrangement around the backbone in Z-DNA, in contrast to the smooth helical
conformations of the more common B-DNA.3 Therefore, although the properties of the glycosidic
bond agree with those of A and B DNA, the alternation in anti and syn conformations are
responsible for the twisted phosphate group conformations. Z-DNA is therefore another example
Spore 8.
of secondary structures that the DNA helix can form depending on the base sequences because the
bases are twisted with respect to one another.
The helical twists for two base pair sequences are different depending on the CG or GC sequence,
which involve very specific helical rotations because of asymmetry in the guanosine and cytidine
conformations. The CG sequence forms a very small twist with no base packing. Because of the
alternating anti-syn glycosidic angles, the base pairs are not positioned astride the helical axis like BDNA. Instead, the edges of the base pairs of Z-DNA are at the surface of the helix.3 The N7 and C8
atoms of the purine ring of guanine and, to a lesser extent, the C5 atom of cytosine actually protrude
on the helical surface. This results in the surface of the helix becoming more convex at these points.
Therefore, Z-DNA has no major grooves. The minor groove is extremely deep and nearly
inaccessible, lined with phosphate groups. The significance of this duplex of two anti-parallel
hexamer strands is that the sugar phosphate backbone typically twists to the right as in A and BDNA. In Z-DNA, the G and C bases have distinct conformations, which results in the zigzag of the
phosphate groups.3 The results of the base pairs protruding on the surface of the helix can be seen
in the Z-DNA molecule of Figure 4.
X-ray Crystallography of Z-DNA structures has shown the helix to have a 44.6 Å pitch with 12 base
pairs per helical turn (in contrast to B-DNA that has 10 base pairs per helical turn). The diameter is
18 Å, slimmer than B-DNA, which is known to have a diameter of about 20 Å.3 Figure 5 shows the
structural differences between A, B, and Z-DNA.
Spore 9.
Figure 4. This Z-DNA model shows the base pairs protruding from the
surface of the helix as a result of the alternating syn and anti-guanosine
conformations.5
Figure 5. Structural differences between B, A, and Z-DNA (shown left to right).3
Spore 10.
Physiological Significance of Z-DNA
Z-DNA is susceptible to attack by several electrophilic compounds. The accessibility of the C8 and
N7 on the guanine renders it susceptible to attack. The N7 is not as susceptible to attack as the C8.
Examples include n-aryl carcinogens, acetylaminofluorines, and C-8 bromination. These stabilize the
Z-DNA helix and promote the B to Z transition. Z-DNA tracts within a genome are now thought
to act as mutational hot spots.3 Z-DNA in the linear form is much less stable than the A and B
DNA forms. Z-DNA in the linear form is most common among prokaryotes.
Z-DNA is now thought to exist in environments with high acidity and high salt concentrations.
Conformational diffraction studies showed that on poly (dG-dC) chains, increasing salt
concentrations beyond 4M NaCl, the spectrum became inverted from its standard B-DNA
associated shape. This major structural change that was found resulted from a Z-DNA
conformation. X-ray techniques have also found evidence of Z-DNA.3
Z-DNA Binding Proteins
In 1994, the function of Z-DNA binding proteins was not known, and therefore the research with
Z-DNA binding proteins is very recent. Proteins that bind Z-DNA stabilize the Z-DNA structure
and have biological significance for the protein.7 For example, Adenosine Deaminase Acting on
RNA (ADAR1), is a 136 kDa double-stranded RNA binding protein. ADAR1 is a member of the
Z family of the Z-DNA binding proteins. Another example of a Z-DNA binding protein is the
Dorso-Longitudinal Muscle protein (DLM-1), a tumor stroma and activated macrophage protein,
which is known for its presence in tumor-related diseases. Both of these proteins have similar Nterminal domains, which is the point on the protein where the Z-DNA binds.8 These similar N-
Spore 11.
terminal domains consist of helix-turn-helix structures that each have an additional  sheet.
Although the structures of the N-terminal domains of ADAR1 and DLM-1 are very similar, the
sequences for the N-domain are not conserved among them, except for the specific regions where
contact with the Z-DNA is made. Therefore, although the sequences may have slight differences,
they are shown to be interchangeably functional when exploring the mutations in the ZDNA/protein complex.9 Figure 6 shows the interaction between ADAR1 and Z-DNA.
Figure 6. The interaction between ADAR1 and Z-DNA.8
In Figure 6, the protein and Z-DNA interaction is shown, indicating various amino acids that interact
with the Z-DNA to form the complex. The Z-DNA/protein complex is stabilized by electrostatic
and Van Der Waals forces. One example of a common characteristic of ADAR1 is the Tyr 177 that
Spore 12.
is shown below that interacts via Van Der Waals forces with the purine base guanine 4, as shown as
G4 on the diagram. In addition, the prolines 192 and 193 interact with the Z-DNA backbone via
Van Der Waals forces to form the protein- Z-DNA complex.8
E3L is a Viral Protein Expressed During Infection:8
Similar to ADAR1 and DLM-1, E3L is a Z-DNA binding protein that is found to be essential for
the pathenogenesis of the vaccinia virus.8,1 E3L encodes a viral protein of 25-kDa that has two
domains called the N-terminal domain and the C-terminal domain. As in ADAR1 and DLM-1, E3L
is a member of the Z family of the Z-DNA binding domains. Figure 7 shows the similarities
between the three different Z-DNA binding proteins. The Z-DNA related domains, Z and Z, are
shown along with the dsRNA binding domain regions.
Figure 7. Three families of proteins are shown, with the domains represented
as colored boxes. The Z-DNA related domains, Z and Z, are shown
along with the dsRNA binding domain regions.8
1
The Vaccinia Virus. Vaccinia is a large poxvirus that contains DNA, replicating within the cytoplasm of
the cell.3 The vaccinia virus causes major changes within the host cell’s machinery shortly after infection. The
vaccinia virus could be a result of genetic recombination. The virus also has been thought to cause a disease
derived from the cowpox virus or the variola virus. Another hypothesis about the vaccinia virus is that it is
the survivor of a now extinct virus. The vaccinia virus was once used for smallpox vaccinations via
inoculation into the skin of the upper arm. However, when the smallpox virus began to spread, routine
vaccination with the vaccinia virus ceased to occur because of its lack of effectiveness. Recent interest in
vaccinia has focused on its possible usage as a vector for immunization against other viruses, which are much
less virulent than the strains used for the smallpox vaccination. This has been done to hopefully reduce any
complications that could occur as a result of strong concentrations of the vaccinia virus being injected into
the body. The deadly consequences of the vaccinia virus are shown through the injection of a mouse with the
virus. If a mouse is injected with a strain of the vaccinia virus, the mouse dies in approximately one week.3
Spore 13.
The N-terminal domain is similar to the Z-DNA binding domains of both ADAR-1 and DLM-1.
The C-terminal domain is a double stranded RNA binding domain that is not required for
replication of the protein. The vaccinia virus has conserved the features of many orthopox viruses.a
When the N-terminal and C-terminal E3L domains of the vaccinia virus and variola virus, an agent
of smallpox, are compared, the domains are almost exactly identical.6
E3L accumulates in the nucleus when expressed by the HeLa cells infected with the vaccinia virus.
In mice, both the N-terminal and C-terminal domains are required for infection. It has been
suggested that the N-terminal domain of E3L is involved in the direct inhibition of the protein
kinase R (PKR) activation. A vaccinia virus mutant lacking E3L induces apoptosis, destroying the
chance for the virus to survive within the host cell. The Z-DNA binding domain of the E3L protein
in HeLa cells was found to localize itself within the nucleus of HeLa cells infected with the vaccinia
virus. HeLa cells that were used in the experiment are an immortal cell line used in medical research,
which were derived from cervical cancer cells.
Nuclear Localization of E3L and its Z-DNA Binding Region8
To confirm where E3L was localized within a cell, the location of E3L was found using confocal
immunofluorescence microscopy with the use of an anti-E3L antibody. As Figure 8 shows, it was
confirmed that Z-DNA is localized within the nucleus in HeLa cells that were infected with the
vaccinia virus. The experiment tested for the localization of the C-terminus using an anti-FLAG
tagged E3L by using direct immunoflorescence microscopy with an anti-FLAG antibody (slides a-f
of Figure 8). The results of this investigation showed the presence of the C-terminus throughout the
Spore 14.
cytoplasm and nucleus of the transfected HeLa cells. Next, the same slides were stained with DAP1
(slides 1-6 of Figure 8) for nuclear counterstaining. The result of this investigation showed nuclear
accumulation of the E3L N-terminal domain specifically, showing the Z-DNA binding region by
itself having a nuclear accumulation within the HeLa cells.
Figure 8. Confocal immunofluorescence was used with an anti-E3L
antibody to find the location of E3L in HeLa cells.8
Hygromyocin B Induces Apoptosis of HeLa Cells in a Dose and Time Dependent Manner8
Apoptosis and Apototic Pathways
Apoptosis is a term for programmed cell death. Apoptosis is necessary for the health of all
organisms, and it is one of the most important defense mechanisms. Apoptosis contributes to the
homeostasis of tissues and remodeling during development. Viruses interfere with apoptosis. The
inhibition of anti-apoptotic pathways is thought to be a major mechanism against viral persistance
because this inhibition will not allow viruses to replicate. A common apoptotic pathway is the p53-
Spore 15.
dependent pathway. The p53 protein has the ability to sense damage that is done to cells and is
therefore a very common apoptotic pathway. The p53 protein then either induces repair of the
DNA or activates the apoptotic pathway as shown in Figure 9.
Figure 9. DNA damage results in increased p53 protein that produces the cell
cycle to be arrested. DNA repair takes place, if possible, or apoptosis occurs.10
One of the mechanisms of the p53 mediated apoptosis is that apoptosis involves the loss of the
mitochondrial membrane and is then followed by release of cytochrome C into the cytosol, which
then leads to activation of caspase cleavage. These events occur because of increased p53 levels
within the cell that have responded to the DNA damage. Another mechanism of p53-mediated
apoptosis involves reactive oxygen species that create mitochondrial damage and apoptosis, which
are induced by p53.11
Hygromycin B 12
Hygromyocin B is an aminoglycoside antibiotic that is commonly used to establish mammalian cell
lines carrying a bacterial gene conferring resistance to the drug. Aminoglycoside antibiotics are
Spore 16.
known to be inhibitors of cell growth by inhibiting protein synthesis in both prokaryotes and
eukaryotes. These inhibitors such as Hygromycin B are often used in selection strategies for
expression of transfected genes due to the introduction of a bacterial gene vector that has resistance
to a specific antibiotic.8 Hygromyocin B is shown to induce apoptosis within the Chinese hamster
ovary LR73 cells, but this apoptotic response does not require the use of the p53 protein.
Hygromyocin B belongs to a p53 independent pathway. Although the mechanism of this p-53
independent pathway is not known, it has been proven that Hygromycin B can induce apoptosis
without p53. Using p53A proved this, which is a cell line derived from baby rat kidney cells that will
express a mutant form of p53 that is temperature sensitive. At the desired temperature, the wild-type
p53 is expressed which causes the cell to die. But when the temperature is raised above the desired
level to 38 C, then only the mutant form of p53 is expressed.12 In this mutant form, the cells are
resistant to p-53 dependent apoptosis. But when Hygromycin B is added to these cells, the cells died
within 47-72 hours. Without the added Hygromycin B, they remained completely viable.12 Therefore,
Hygromycin B puts into effect a p-53 independent apoptotic pathway. Hygromyocin B induces
apoptosis in many viral proteins, but it was examined to see hygromycin-induced apoptosis was also
the case in HeLa cells.
Knowing that apoptosis is an important defense mechanism, the inhibition of this process within a
cell is a crucial step for the life of a virus. To determine whether or not hygromyocin B was inducing
apoptosis in HeLa cells via the p53 independent pathway, the cell viability of samples were observed
by trypan blue exclusion.8 The trypan blue dye exclusion test is used to determine the number of
viable cells present in a cell suspension. The procedure is based on the principle that live cells
possess intact cell membranes that exclude certain dyes, such as trypan blue, Eosin, or propidium,
Spore 17.
whereas dead cells do not. It was found that hygromyocin induced apoptosis in a dose and timedependent manner. As Figure 10 shows, the cell viability decreased by 50% after 12 hours with 800
micrograms per mL of hygromyocin B.
Figure 10. Hygromyocin-induced apoptosis of HeLa cells.8
Most of the cells died after 24 hours. To confirm whether the cells’ viability decreased from
apoptosis, the cell morphologies were examined. Using phase contrast microscopy at 12, 18, 24, and
48 hours, the HeLa cells displayed characteristics of apoptosis, including disintegrating cell
membrane, nuclear condensation, and loss of cellular processes. DNA fragmentation analysis using
gel electrophoresis was also used to study the apoptotic effect of hygromyocin B on the HeLa cells.
Spore 18.
The fragmentation analysis shown on Figure 10B also showed that the hygromyocin B-treated HeLa
cells lost viability in a dose and time-dependent manner.8
E3L Inhibits Hygromyocin-B Induced Apoptosis of HeLa Cells by Z-DNA Binding8
It was next examined whether or not E3L had an effect on the apoptotic effect of hygromyocin B
that was previously proven in the HeLa cells. HeLa cells were transfected with an E3L expression
plasmid, from the vaccinia virus, or an empty vector in response to hygromyocin B by trypan blue
staining. As shown in Figure 11, the E3L-infected HeLa cells were protected from the apoptotic
effects of the hygromyocin B. In Figure 11A, the results of the E3L effect on the HeLa cells can be
seen because there is a great decrease in cell viability within the control group in contrast to the
HeLa cells containing E3L. These results are the same when the concentration and time of injection
of the hygromyocin is displayed. Also, the inhibition effect of E3L disappeared when the 83 Nterminal amino acids of the E3L were deleted (shown as the blue lines on each of the graphs of part
A). This result alludes to the involvement of the Z-DNA binding domain to the anti-apoptotic effect
of the E3L. The cell morphologies using phase-contrast microscopy were also used to determine
anti-apoptotic activity, which confirmed the results shown in Figure 11.
The importance of the Z-DNA binding region in the anti-apoptotic effects of E3L were
examined by assembling various plasmids containing insertions or deletions to E3L. These changes
included deletions in the N-terminal and C-terminal domains. Point mutations were also used to
examine the significance of the Z-DNA binding domain. As shown in Figure 11, 1-83 E3L and 472 E3L are lacking the entire N-terminal region or solely the Z-DNA binding domain, respectively.
Deletions of these regions caused hygromyocin to be able to induce apoptotic activity.8
Spore 19.
Figure 11. Hygromyocin-B induced apoptosis of HeLa cells.8
Spore 20.
Point mutations that were introduced to examine the role of the Z-DNA binding domain (Y148A
E3L and P63A E3L) failed to prevent apoptosis by the hygromyocin B. When the C-terminus was
deleted from the E3L (shown as 106-190 and 117-182 in Figure 11), the anti-apoptotic effect
remained in the HeLa cells. The 106-190 region contains the entire C-terminus while the 117-182
region contains only the RNA-binding region of the C-terminal region. The results of these
deletions were similar to the results using the wild type of E3L. Only the N-terminus containing the
Z-DNA binding region had an effect on inhibiting the anti-apoptotic effect of the E3L when the Nterminal region was deleted. This finding suggests the involvement of the Z-DNA binding region of
the N-terminus with the efficiency of the anti-apoptotic effect of E3L.8
Another part of the experiment involved the replacement of the N-terminal domain of the
E3L with the N-terminal domain of the ADAR1 to see whether or not the pathogenic effect of this
replacement would be similar. This conversion to a different but similar N-terminal domain
displayed the same level of anti-apoptotic effect as the E3L wild type.
Conclusion
The crystal structural features along with the biological aspects of Z-DNA were examined in
order to evaluate the biochemical relevance to the alternative DNA structures. Z-DNA has a
biological role of binding to proteins through the N-terminus in order to not only stabilize the ZDNA structure but to also activate the protein expression. One example of a Z-DNA binding
protein is E3L, essential to the parthenogenesis of the vaccinia virus. It was shown that E3L
accumulates within the nucleus of HeLa cells, and the Z-DNA binding domain is also localized
solely within the nucleus. Hygromyocin B was shown to induce apoptosis (programmed cell death)
in HeLa cells. E3L inhibits the hygromyocin-B induced apoptosis. The Z-DNA binding activity of
the N-terminal domain of the E3L protein was found to be necessary for the vaccinia virus
Spore 21.
pathenogenesis. From the results, it is clear that Z-DNA binding is essential for the effects and
sustainability of the vaccinia virus. The mechanism of this process is yet to be determined. It is
suspected that because of the torsional strain of the Z-DNA molecule, binding to the protein
stabilizes the Z-DNA molecule.
Future directions include finding a small molecule that could interfere with the binding of
E3L to Z-DNA and could possibly prevent the pathenogenesis of such diseases as the vaccinia virus
and other viruses that have proteins stimulating anti-apoptosis activity.13 These antiviral agents could
be responsible for decreasing the deleterious effects of many orthopox viruses. Successful treatment
options could be a result of such antiviral agents that prevent the effects for proteins binding the ZDNA.
Spore 22.
References
(1) Olby, R. Nature 2003, 421, 513.
(2) Berg, J.; Tymoczko, J.; Stryer, L. DNA replication repair, and recombination; In Biochemistry; WH
Freeman and Company: New York, 2007; pp. 783-816.
(3) Neidle, S. DNA structure as observed in fibres and crystals; In DNA Structure and Recognition;
Rickwood D. Ed. Oxford University Press Inc.: New York, 1994; pp. 29-54.
(4) Dang, L.X.; Pearlman, D.A.; Kollman P.A. Proc. Natl. Acad. Sci. USA 1990, 88, 4630.
(5) http://gibk26.bse.kyutech.ac.jp/jouhou/image/nucleic/dna/zdna_st.small.gif
(6) Wang, G.; Christensen, L.; Vasquez, K. Proc. Natl. Acad. Sci. USA 2006, 103, 2677.
(7) Kim, Y.; Muralunath M.; Brandt T.; Pearcy M.; Hauns K.; Lowenhaupt K.; Jacobs B.; Rich A.
Pro. Natl. Acad. Sci. USA 2003, 100, 6974.
(8) Kwon, J.; Rich, A. Proc. Natl. Acad. Sci. USA 2005, 102, 12764.
(9) Kim, Y.; Muralunath M.; Brandt T.; Pearcy M.; Hauns K.; Lowenhaupt K.; Jacobs B.; Rich A.
Pro. Natl. Acad. Sci. USA 2003, 100, 6974.
(10) http://www.portfolio.mvm.ed.ac.uk/studentwebs/session2/group28/p53.html
(11) Ha, S.; Lokanth N.K.; Quyen D.V.; Wu, C.; Lowenhaupt, K.; Rich A.; Kim, Y.; Kim, K. Proc.
Natl. Acad. Sci. USA 2004, 101, 14367.
(12) Chen, G.; Brandton, P. E.; Shore, G.C. Exp. Cell Res. 1995, 221, 55.
(13) Pennisi, E. Science 2006, 312, 1467.