Dbf4p, an essential S phase-promoting factor, is targeted for degradation by the anaphase-promoting complex.
The Dbf4p/Cdc7p protein kinase is essential for the activation of replication origins during S phase. The catalytic subunit, Cdc7p, is present at constant levels throughout the cell cycle. In contrast, we show here that the levels of the regulatory subunit, Dbf4p, oscillate during the cell cycle. Dbf4p is absent from cells during G(1) and accumulates during the S and G(2) phases. Dbf4p is rapidly degraded at the time of chromosome segregation and remains highly unstable during pre-Start G(1) phase. The rapid degradation of Dbf4p during G(1) requires a functional anaphase-promoting complex (APC). Mutation of a sequence in the N terminus of Dbf4p which resembles the cyclin destruction box eliminates this APC-dependent degradation of Dbf4p. We suggest that the coupling of Dbf4p degradation to chromosome separation may play a redundant role in ensuring that prereplicative complexes, which assemble after chromosome segregation, do not immediately refire.
Ferreira
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MF
ICRF Clare Hall Laboratories, South Mimms EN6 3LD, United Kingdom.
Santocanale
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C
Drury
L S
LS
Diffley
J F
JF
D000705:Anaphase / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics*; D005656:Fungal Proteins / Q000235:genetics*; D015966:Gene Expression Regulation, Fungal; D010750:Phosphoproteins / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D016196:S Phase / Q000235:genetics*; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins
D018797:Cell Cycle Proteins; C088096:Dbf4 protein, S cerevisiae; D005656:Fungal Proteins; D010750:Phosphoproteins; D029701:Saccharomyces cerevisiae Proteins; C489404:CDC7 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases