Mutations in the SPT4, SPT5, and SPT6 genes alter transcription of a subset of histone genes in Saccharomyces cerevisiae.

The SPT4, SPT5, and SPT6 gene products define a class of transcriptional repressors in Saccharomyces cerevisiae that are thought to function through their effects on chromatin assembly or stability. Mutations in these genes confer a similar range of phenotypes to mutations in HIR genes, which encode transcriptional repressors that regulate expression of many of the core histone genes. Here we show that mutations in the three SPT genes also affect transcription of the histone genes that reside at the HTA1-HTB1 locus. HTA1-lacZ transcription was reduced in each spt mutant background, an effect that required a negative site in the HTA1 promoter. The transcriptional effect could be reversed by the overproduction of histones H2A and H2B in an spt4 mutant and histones H3 and H4 in all three spt mutants. Suppression of the spt4 transcriptional defect was dependent on the overproduction of both histones H2A and H2B, and required the presence of N-terminal amino acids in both histones. The results are consistent with the idea that the effects of the spt mutations on nucleosome assembly and/or stability activate repressors of HTA1 transcription.