G1
iv
d
ll
ce
n
o
i
is
collating
machine
xerox
machine
DNA replication
S
DNA
chromosome
segregation
M
G2
Alternation of DNA replication and chromosome segragation
DNA replication
+
chromosome segregation
The logic of the cell cycle:
cell fusion experiments (Rao & Johnson)
S phase cells contain
a factor that can trigger
DNA replication in G1 cells:
S phase Promoting Factor
The logic of the cell cycle:
cell fusion experiments (Rao & Johnson)
block of re-replication
The Cell Division Cycle
2
mass
growth
1
2
1
DNA
nucleus
division
Balanced growth and division
TC = cycle time
Cytoplasmic mass
4
TD= mass doubling time
TC > TD
3
2
TC = TD
1
TC < TD
0
0
1
2
time
3
4
Chromosome cycle
Growth cycle
- cytoplasmic growth
- DNA replication
- cell division
- mitosis
(approx. doubling
(precise replication
and halving)
and segregation)
Dissociation of growth and chromosome cycle
Oogenesis
Embryogenesis
Saccharomyces cerevisiae
Lee Hartwell
Isolation of temperature sensitive cdcts mutants
Phenotype of cdc mutants
asynchronous
culture
cdc mutant
with problem of
mitotic exit
Cdc28 is responsible for the first genetically controlled event
cdc28
Cloning of cdcts genes
Cdc28 is a protein-kinase
Schizosaccharomyces pombe
G1
S
M
G2
Sir Paul Nurse
Murdoch Mitchison
wee1ts
wildtype
cdc2ts
cdc25ts
cdc13ts
wee1ts
wee2ts = cdc2D
wildtype
cdc2ts
cdc25ts
cdc13ts
cdc2 is required at two points
during the cell cycle
cdc2
cdc28S.c. and cdc2S.p. are functional homologs
Do human cells have the same gene?
Nature, Vol, 327, No. 6117, pp. 31-35, May 7, 1987
Melanie Lee
Cell, Vol. 45: 145-153, April 11, 1986
Cell, Vol. 49: 559-567, May 22, 1987
inject cytoplasm
Yoshio Masui, Ph.D., FRS
Professor Emeritus of Zoology
University of Toronto
Ontario, Canada
Yoshio Masui, Ph.D., FRS
Professor Emeritus of Zoology
University of Toronto
Ontario, Canada
Periodic proteins (cyclins)
during early embryonic development
Tim Hunt
Western
Jim Maller
IP
MPF is a cyclin-dependent protein-kinase
Cdk1
CycB
Cyclin and MPF levels during early mitotic cycles
Questions:
What causes the fast disappearance of cyclins?
What is the reason of the delay between cyclin
and MPF?
Cycling cell free extract
Anaphase Promoting Complex or Cyclosome
chromosome
segregation
C
d
c
2 AP
C
0
Kim Nasmyth
Anaphase Promoting Complex or Cyclosome
chromosome
segregation
C
d
c
2 AP
C
0
Cdk1
CycB
CycB degradation
Cdk1
+
degraded
CycB
The G2/M transition is regulated
by post-translational modification
P
Cdk1
CycB
inactive
(preMPF)
Wee1
Cdc25
Cdk1
CycB
active
(MPF)
Wee1 is a tyrosine-kinase
Cdc25 is a tyrosine-phopshatase
Start of DNA replication is also controlled by proteolysis
degraded
CKI
cyclin
inactive
Cdk/cyclin
complex
P
Cdk
cyclin
phosphorylated
CKI
CKI
Cdk
CKI
CKI
G1
Cdk
cyclin
multiubiquitaned
CKI
Cdk
cyclin
active
Cdk/cyclin
complex
Regulation of CDK activity
Cyclin
Cdk
Cdk
Cyclin
Cyclin
CKI
Cdk
Cdk
Cyclin
CKI
P