Chromatin-mediated transcriptional regulation by the yeast architectural factors NHP6A and NHP6B

The Saccharomyces cerevisiae NHP6A and NHP6B proteins are chromatin archite ctural factors, functionally and structurally related to the mammalian high mobility group (HMG)-1 and -2 proteins, a family of non-sequence-specific DNA binding proteins. nhp6a nhp6b mutants have various morphological defect s and are defective in the induced expression of several RNA polymerase II- transcribed genes. We found that NHP6A/B proteins are also required for ful l induction of the yeast CHA1 gene. Importantly, CHA1 basal level expressio n is increased 10-fold in an nhp6a nhp6b double deletion mutant. Micrococca l nuclease and DNase I analysis of the CHA1 gene in this strain showed an o pen promoter structure, characteristic of the activated state of this promo ter, even under noninducing conditions. To address the possible function of the NHP6A/B proteins in chromatin-mediated gene regulation, we performed w hole-genome transcriptional profiling of a Delta nhp6a Delta nhp6b yeast st rain. Our results suggest that NHP6A/B proteins play an important regulator y role, repressing as well as potentiating expression of genes involved in several cellular processes, and that NHP6A/B control is exerted at the leve l of the individual gene.