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Molecular and Cellular Biology, January 2000, p. 242-248, Vol. 20, No. 1
ICRF Clare Hall Laboratories, South Mimms EN6
3LD, United Kingdom
Received 8 February 1999/Returned for modification 8 July
1999/Accepted 1 October 1999
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 G1
and accumulates during the S and G2 phases. Dbf4p is rapidly degraded at the time of chromosome segregation and remains highly unstable during pre-Start G1 phase. The rapid
degradation of Dbf4p during G1 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.
0270-7306/0/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Dbf4p, an Essential S Phase-Promoting Factor, Is
Targeted for Degradation by the Anaphase-Promoting Complex
*
Corresponding author. Mailing address: ICRF Clare Hall
Laboratories, South Mimms, Herts. EN6 3LD, United Kingdom. Phone:
44-171-269-3869. Fax: 44-171-269-3801. E-mail:
J.Diffley{at}icrf.icnet.uk.
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