Decreased expression of specific genes in yeast cells lacking histone H1.

Chromatin plays an important role in regulating eukaryotic gene expression. Chromatin is composed of DNA wrapped around a nucleosome core (consisting of two copies of the well conserved histones H2A, H2B, H3, and H4) and a more variable linker histone H1. Various in vitro and in vivo studies have implicated histone H1 as a repressor of gene expression or as an activator, but its exact role is still unclear. Sequencing of the yeast genome has led to the identification of a putative histone H1 gene. Biochemical studies demonstrated that yeast does indeed possess a bona fide histone H1. However, deletion of the unique yeast H1 gene is not associated with any phenotypes, and it was questioned whether it plays any role. To address this issue, we performed whole-genome microarray analysis to identify genes that are affected by H1 removal. Surprisingly, deletion of the gene encoding histone H1 does not result in increased gene expression but rather in a modest reduction. Northern blot analysis of selected genes confirmed the results obtained with the microarray analysis. A similar effect was observed with an integrated lacZ reporter. Thus, our data demonstrate that removal of yeast histone H1 only results in decreased gene expression.