ABSTRACT
Checkpoints monitor the successful completion of cell cycle processes, such as DNA replication, and also regulate the expression of cell cycle-dependent genes that are required for responses. In the model yeast Schizosaccharomyces pombe G 1/S phase-specific gene expression is regulated by the MBF (also known as DSC1) transcription factor complex and is also activated by the mammalian ATM/ATR-related Rad3 DNA replication checkpoint. Here, we show that the Yox1 homeodomain transcription factor acts to co-ordinate the expression of MBF-regulated genes during the cell division cycle. Moreover, our data suggests that Yox1 is inactivated by the Rad3 DNA replication checkpoint via phosphorylation by the conserved Cds1 checkpoint kinase. Collectively, our data has implications for understanding the mechanisms underlying the coordination of cell cycle processes in eukaryotes.
Subject(s)
Cell Cycle Proteins/metabolism , Cell Cycle , DNA Replication , Gene Expression Regulation, Fungal , Homeodomain Proteins/metabolism , Schizosaccharomyces pombe Proteins/metabolism , Schizosaccharomyces/genetics , Schizosaccharomyces/metabolism , Transcription Factors/metabolism , Ataxia Telangiectasia Mutated Proteins , Cell Cycle Proteins/genetics , Checkpoint Kinase 2 , DNA, Fungal/genetics , DNA, Fungal/metabolism , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , Homeodomain Proteins/genetics , Phosphorylation , Protein Kinases/genetics , Protein Kinases/metabolism , Protein Serine-Threonine Kinases/genetics , Protein Serine-Threonine Kinases/metabolism , Schizosaccharomyces/cytology , Schizosaccharomyces pombe Proteins/genetics , Transcription Factors/genetics , Tumor Suppressor Proteins/genetics , Tumor Suppressor Proteins/metabolismABSTRACT
The fission yeast HIRA proteins Hip1 and Slm9 are members of an evolutionarily conserved family of histone chaperones that are implicated in nucleosome assembly. Here we have used single-step affinity purification and mass spectrometry to identify factors that interact with both Hip1 and Slm9. This analysis identified Hip3, a previously uncharacterized 187-kDa protein, with similarity to S. cerevisiae Hir3. Consistent with this, cells disrupted for hip3+ exhibit a range of growth defects that are similar to those associated with loss of Hip1 and Slm9. These include temperature sensitivity, a cell cycle delay, and synthetic lethality with cdc25-22. Furthermore, genetic analysis also indicates that disruption of hip3+ is epistatic with mutation of hip1+ and slm9+. Mutation of hip3+ alleviates transcriptional silencing at several heterochromatic loci, including in the outer (otr) centromeric repeats, indicating that Hip3 is required for the integrity of pericentric heterochromatin. As a result, loss of Hip3 function leads to high levels of minichromosome loss and an increased frequency of lagging chromosomes during mitosis. Importantly, the function of Hip1, Slm9, and Hip3 is not restricted to constitutive heterochromatic loci, since these proteins also repress the expression of a number of genes, including the Tf2 retrotransposons.
