G1

division xerox DNA replication cell machine collating S machine

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 division 2 mass growth

1

2 DNA nucleus

1 Balanced growth and division

TC = cycle time TD= mass doubling time 4

3 TC > TD mass

2

TC = TD

Cytoplasmic 1

TC < TD 0 0 1 2 3 4 time Chromosome cycle Growth cycle - DNA replication - cytoplasmic growth - mitosis - cell division (precise replication (approx. doubling and segregation) and halving) 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

S G1 M

G2

Sir Paul Nurse Murdoch Mitchison cdc2ts cdc25ts wee1ts wildtype cdc13ts cdc2ts ts wee1ts cdc25 wildtype ts wee2ts = cdc2D cdc13 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

IP Jim Maller 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 APC 0

Kim Nasmyth Anaphase Promoting Complex or Cyclosome

chromosome segregation

C d c 2 APC 0

Cdk1 Cdk1 CycB CycB degradation + degraded CycB The G2/M transition is regulated by post-translational modification

Wee1 P Cdk1 Cdk1 CycB CycB Cdc25 inactive active (preMPF) (MPF)

Wee1 is a tyrosine-kinase Cdc25 is a tyrosine-phopshatase Start of DNA replication is also controlled by proteolysis

degraded CKI G1

Cdk P Cdk Cdk CKI CKI CKI cyclin cyclin cyclin

inactive Cdk phosphorylated multiubiquitaned Cdk/cyclin CKI CKI cyclin complex active Cdk/cyclin complex Regulation of CDK activity

Cyclin

Cdk

P Cdk Cdk Cyclin Cyclin

Cdk CKI Cyclin CKI