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Abstract
The packaging of DNA into chromatin prevents access of the machinery necessary to regulate DNA replication and gene expression. The structure of chromatin provides regulatory flexibility through the occurrence of post-translational modifications of histone proteins, such as acetylation and phosphorylation, to activate cellular processes, such as replication and transcription. I have investigated the roles of covalent histone modifications in both of these processes in the yeast Saccharomyces cerevisiae. I have explored whether histone acetylation at origins of replication coincides with the timing of initiation of replication, using the method of chromatin immunoprecipitation (ChIP). Preliminary results of this work are presented here. I have also addressed the role of histone H2A in the transcription of CUP1, a gene induced in response to toxic levels of copper. Histones H3 and H4 are acetylated during CUP1 gene expression, and this acetylation requires the protein Spt10. I have shown that specific H2A mutations in combination with spt10 deletions result in aberrant regulation of CUP1 expression. Specifically, serine mutations in H2A prevent CUP1 shutdown when combined with spt10 deletions. In addition, mutants lacking the ATP-dependent chromatin remodeler SWI/SNF exhibit both impaired CUP1 induction and failure to shut down CUP1 normally. These data indicate that CUP1 transcriptional shutdown, like induction, is an active process controlled by the chromatin structure of the gene. These results provide new insights for the role of chromatin structure in metal homeostasis.
