SPT10 AND SPT21 ARE REQUIRED FOR TRANSCRIPTION OF PARTICULAR HISTONE GENES IN SACCHAROMYCES-CEREVISIAE

The Saccharomyces cerevisiae genome contains four loci that encode his tone proteins. Two of these loci, HTA1-HTB1 and HTA2-HTB2, each encode histones H2A and H2B. The other two loci, HHT1-HHF1 and HHT2-HHF2, ea ch encode histones H3 and H4. Because of their redundancy, deletion of any one histone locus does not cause lethality. Previous experiments demonstrated that mutations at one histone locus, HTA1-HTB1, do cause lethality when in conjunction with mutations in the SPT10 gene. SPT10 has been shown to be required for normal levels of transcription of se veral genes in S. cerevisiae. Motivated by this double-mutant lethalit y, we have now investigated the interactions of mutations in SPT10 and in a functionally related gene, SPT21, with mutations at each of the four histone loci. These experiments have demonstrated that both SPT10 and SPT21 are required for transcription at two particular histone lo ci, HTA2-HTB2 and HHF2-HHT2, but not at the other two histone loci. Th ese results suggest that under some conditions, S. cerevisiae may cont rol the level of histone proteins by differential expression of its hi stone genes.