Title: The histone regulatory proteins Spt10 and Spt21
Description: The proper regulation of chromatin structure is critical for the regulation of fundamental cellular processes. SPT10 and SPT21 are two genes involved in regulating the transcription of histone genes in Saccharomyces cerevisiae . While spt10 and spt21 mutants share many transcription defects, spt10 deletion mutants have a much more severe growth defect than spt21 deletion mutants, suggesting that SPT10 plays roles additional to those shared with SPT21 . Furthermore, no growth defect results from deleting HTA2-HTB2 , the histone locus most affected in spt10 and spt21 deletion mutants. In order to gain insight into these differences, in the first research chapter we isolated and characterized suppressors of the spt10 slow growth defect, leading to the unexpected finding that mutants that slow cell cycle progression can actually improve the growth of spt10 mutants. In the second research chapter we characterized the roles of SPT10 and SPT21 in transcriptional silencing. We found that spt10 and spt21 mutants have decreased silencing at telomeres and the silent mating loci, as well as increased silencing at the rDNA. In a molecular analysis at one telomere, we found that the level of Sir protein association shows little or no change, though histone modifications are altered in spt10 and spt21 mutants. However, chromatin structure is perturbed in the region, as well as in a region farther from the telomere. Together, these results suggest that SPT10 and SPT21 play important regulatory roles that may be less of a direct consequence of HTA2-HTB2 transcription regulation but more a product of their global influence on chromatin structure.