engleski

A NOVEL ROLE FOR Gcn5: INCREASING THE RATE OF CHROMATIN REMODELING AND GENE ACTIVATION

Histone acetyltransferases (HATs) such as Gcn5 play a role in transcriptional activation. However, the majorityof constitutive genes show no requirement for GCN5, and even regulated genes, such as the yeast PHO5 gene, do not seem to be affected significantly by its absence under normal activation conditions. Here we show that even though the steady state level of activated PHO5 transcription is not affected by deletion of GCN5, the rate of activation following phosphate starvation is significantly decreased. This delay in transcriptional activation is specifically due to slow chromatin remodeling of the PHO5 promoter, whereas the transmission of the phosphate starvation signal to the PHO5 promoter progresses at normal rate. Chromatin remodeling is equally delayed in a galactose inducible PHO5 promoter variant in which the Pho4 binding sites have been replaced by Gal4 binding sites. By contrast, activation of the GAL1 gene by galactose addition occurs with normal kinetics. These results indicate that one important contribution of HATs is to increase the rate of gene induction by accelerating chromatin remodeling, rather than to affect the final steady state expression levels.

Histone acetylation; GCN5; PHO5; chromatin

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