Functional interaction between GCN5 and polyamines: a new role for core histone acetylation.

Polyamines are organic polycations essential for a wide variety of cellular functions, including nuclear integrity and chromosome condensation. Here we present genetic evidence that depletion of cellular polyamines partially alleviates the defects in HO and SUC2 expression caused by inactivation of the GCN5 histone acetyltransferase. In addition, the combination of polyamine depletion and a sin(-) allele of the histone H4 gene leads to almost complete bypass of the transcriptional requirement for GCN5. In contrast, polyamine depletion does not alter the transcriptional requirements for the SWI/SNF chromatin remodeling complex nor does depletion lead to global defects in transcriptional regulation. In addition to these genetic studies, we show that polyamines facilitate oligomerization of nucleosomal arrays in vitro, and that polyamine-mediated condensation requires intact core histone N-terminal domains and is inhibited by histone hyperacetylation. Our studies suggest that polyamines are repressors of transcription in vivo, and that one role of histone hyperacetylation is to antagonize the ability of polyamines to stabilize highly condensed states of chromosomal fibers.