HISTONE ACETYLTRANSFERASE ACTIVITY AND INTERACTION WITH ADA2 ARE CRITICAL FOR GCN5 FUNCTION IN-VIVO

Yeast GCN5 is one component of a putative adaptor complex that include s ADA2 and ADA3 and functionally connects DNA-bound transcriptional ac tivators with general transcription factors. GCN5 possesses histone ac etyltransferase (HAT) activity, conceptually linking transcriptional a ctivation with enzymatic modification at chromatin. We have identified the minimal catalytic domain within GCN5 necessary to confer HAT acti vity and have shown that in vivo activity of GCN5 requires this domain . However, complementation of growth and transcriptional activation in gcn5(-) cells required not only the HAT domain of GCN5, but also inte raction with ADA2. The bromodomain in GCN5 was dispensable for HAT act ivity and for transcriptional activation by strong activators; however , it was required for full complementation in other assays. Fusion of GCN5 to the bacterial lexA DNA binding domain activated transcription in vivo, and required both the HAT domain and the ADA2 interaction dom ain, These results suggest that both functions of GCN5, HAT activity a nd interaction with ADA2, are necessary for targeting and acetylation of nucleosomal histones.