title: Genetic interactions between CDC7 and CDC28: growth inhibition of cdc28-1N by Cdc7 point mutants.
abstract: BACKGROUND
  Cdc7 kinase of Saccharomyces cerevisiae, a nuclear phosphoprotein, regulates initiation of chromosomal DNA replication. Overexpression of kinase-negative Cdc7 point mutants (T281E, D182N and D163N) arrests the cell cycle of the wild-type Saccharomyces cerevisiae cells at the G1/S boundary. This is caused by titration of a regulatory protein, Dbf4, from the wild-type Cdc7, which leads to inactivation of its kinase activity.
  
  
  RESULTS
  We report here that kinase-negative Cdc7 mutants, when overexpressed in cdc28-1N(ts) at a permissive temperature, not only inhibit DNA replication by inactivating the wild-type Cdc7 but may also disturb coordination between DNA replication and cell division. Suppression of growth inhibition under this condition requires co-expression of both Dbf4 and Cdc28, whereas Dbf4 alone can counteract the growth inhibition in the wild-type cells. In cdc28-1N(ts), co-expression of the wild-type Dbf4 rescues only the G1/S defect and results in accumulation of those cells with less than 1C DNA as well as 2C DNA. On the other hand, co-expression of Cdc28 alone leads to increase of those cells arrested at the G1/S boundary, as found typically in the wild-type. We also report that overexpression of T281A, a 'weak' allele of Cdc7, causes growth arrest in cdc28-1N(ts) cells, but not in the CDC28 wild-type cells. This suggests that T281A is inactive in cdc28-1N(ts) and is consistent with the idea that Cdc28 activates Cdc7 by phosphorylation.
  
  
  CONCLUSIONS
  We conclude that two essential serine-threonine kinases, Cdc28 and Cdc7, genetically interact for initiation of the S phase and possibly for G2/M progression and/or S phase checkpoint control.
authors.affiliation: Department of Molecular and Developmental Biology, Institute of Medical Science, The University of Tokyo, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Ohtoshi
authors.forename: K
authors.initials: K
authors.lastname: Arai
authors.forename: H
authors.initials: H
authors.lastname: Masai
mesh_terms: D017489:CDC28 Protein Kinase, S cerevisiae / Q000235:genetics*; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000235:genetics; D004261:DNA Replication / Q000235:genetics; D016193:G1 Phase; D010641:Phenotype; D010750:Phosphoproteins / Q000235:genetics*; D011003:Ploidies; D017354:Point Mutation; D011494:Protein Kinases / Q000235:genetics*; D017346:Protein Serine-Threonine Kinases; D016196:S Phase; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins; D013696:Temperature
chemical_list: D018797:Cell Cycle Proteins; D010750:Phosphoproteins; D029701:Saccharomyces cerevisiae Proteins; D011494:Protein Kinases; C489404:CDC7 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; D017489:CDC28 Protein Kinase, S cerevisiae