Control by RNA
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Lilli Howard
BIOL/GEN 313
Dr. Rodermel/Dr. Tuggle
11/5/14
1. Name the two mechanisms by which RNA regulates the expression of bacterial genes.
Antisense RNAs (microRNAs), using ompF expression as a model
Riboswitches
2. Describe OmpF expression. Which kind of regulation is this? Antisense RNA
1. OmpF (outer membrane protein F) is a protein that forms a plasma membrane
channel for ions, water to pass through
2. ompF gene expression is regulated by osmolarity (solute concentration difference
between the external medium and the cell)
If a high solute concentration outside cell versus a low solute concentration inside
(high osmolarity), OmpF is not made, and hence there are no channels for water to
leave the cell (water diffusion out of cell would make the cell shrivel up, so you want
to retain water!)
Regulator gene is micF : a small antisense RNA; it is complementary to sequences in 5’-UTR
of the sense mRNA. When osmolarity is high, it binds so that ompF cannot be made.
3. When activated, riboswitches (activate/inhibit) translation. How do these work?
Riboswitches are regulatory sequences in an mRNA (usually in the 5’-UTR); these
sequences form a specific secondary structure in the presence of a regulatory molecule
(usually a protein)
This secondary structure often contains a Shine Dalgarno sequence that is not accessible
to a ribosome, hence, translation is inhibited (translational control)
4. Antisense RNA is complementary to other RNA or DNA sequences.
5. If you wanted to inhibit the transcription of a bacterial gene with antisense RNA, what
sequences might the antisense RNA contain? Promoters, consensus sequences, etc.
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REVIEW
6. The following chart shows the presence or absence of arabinose isomerase, an enzyme, as
a result of experiments performed in the presence or absence of arabinose.
Genotype
Arabinose Absent
Arabinose present
1.
C+ A+
+
- +
2.
C A
3.
C- A+ / C+ A+
4.
CC A- / C- A+
+
+
a. On the basis of the results in the above experiments, is the C gene an operator or a
regulator gene? Explain your reasoning. Regulator, it acts in trans
b. Do these experiments suggest that the arabinose operon is negatively or positively
controlled? Explain your reasoning. Positive
c. What type of mutation is CC? Constitutive expression of the regulator
7. A mutant strain of E. coli produces b-galactosidase in the presence and in the absence of
lactose. Where in the operon might the mutation in this strain be?
Constitutive expression of the operator
8. In what conditions are levels of cAMP high? Low glucose
9. In what conditions are levels of cAMP low? High glucose
1060 Hixson-Lied Student Success Center  515-294-6624  sistaff@iastate.edu  http://www.si.iastate.edu