REPRESSION OF GCN5 HISTONE ACETYLTRANSFERASE ACTIVITY VIA BROMODOMAIN-MEDIATED BINDING AND PHOSPHORYLATION BY THE KU-DNA-DEPENDENT PROTEIN-KINASE COMPLEX

GCN5, a putative transcriptional adapter in humans and yeast, possesse s histone acetyltransferase (HAT) activity which has been linked to GC N5's role in transcriptional activation in yeast. Tri this report, we demonstrate a functional interaction between human GCN5 (hGCN5) and th e DNA-dependent protein kinase (DNA-PK) holoenzyme. Yeast two-hybrid S creening detected an interaction between the bromodomain of hGCN5 and the p70 subunit of the human Ku heterodimer (p70-p80), which is the DN A-binding component of DNA-PK. interaction between intact hGCN5 and Ku 70 was shown biochemically using recombinant proteins and by coimmunop recipitation of endogenous proteins following chromatography of HeLa n uclear extracts. We demonstrate that the catalytic subunit of DNA-PK p hosphorylates hGCN5 both in vivo and in vitro and, moreover, that the phosphorylation inhibits the HAT activity of hGCN5. These findings sug gest a possible regulatory mechanism of HAT activity.