CDC45 is required in conjunction with CDC7/DBF4 to trigger the initiation of DNA replication

CDC45 is required in conjunction with CDC7/DBF4 to trigger the initiation of DNA replication

Department of Microbiology and Immunology, University of California, San Francisco, CA 94143-0414

Communicated by Ira Herskowitz, University of California, San Francisco, CA (received for review July 25, 1997)

Abstract

The initiation of DNA replication in Saccharomyces cerevisiae requires the protein product of the CDC45 gene. We report that although Cdc45p is present at essentially constant levels throughout the cell cycle, it completes its initiation function in late G₁, after START and prior to DNA synthesis. Shortly after mitosis, cells prepare for initiation by assembling prereplicative complexes at their replication origins. These complexes are then triggered at the onset of S phase to commence DNA replication. Cells defective for CDC45 are incapable of activating the complexes to initiate DNA replication. In addition, Cdc45p and Cdc7p/Dbf4p, a kinase implicated in the G₁/S phase transition, are dependent on one another for function. These data indicate that CDC45 functions in late G₁ phase in concert with CDC7/DBF4 to trigger initiation at replication origins after the assembly of the prereplicative complexes.

Footnotes

↵ * To whom reprint requests should be addressed at: Department of Microbiology, Box 0414, University of California, San Francisco, CA 94143-0414. e-mail: jli{at}cgl.ucsf.edu.
ABBREVIATIONS:

ORC,

origin recognition complex;

MCM,

minichromosome maintenance;

pre-RC,

prereplicative complex;

post-RC,

post replicative complex;

HU,

hydroxyurea;

HA,

hemagglutinin