Overlapping roles for the histone acetyltransferase activities of SAGA andElongator in vivo

Elp3 and Gcn5 are histone acetyltransferases (HATs) that function in transc ription as subunits of Elongator and SAGA/ADA, respectively. Here we show t hat mutations that impair the in vitro HAT activity of Elp3 confer typical elp phenotypes such as temperature sensitivity. Combining an elp3 Delta mut ation with histone H3 or H4 tail mutations confers lethality or sickness, s upporting a role for Elongator in chromatin remodelling in vivo. gcn5 Delta elp3 Delta double mutants display a number of severe phenotypes, and simil ar phenotypes result from combining the elp mutation with mutation in a gen e encoding a SAGA-specific, but not an ADA-specific subunit, indicating tha t Elongator functionally overlaps with SAGA. Because concomitant active sit e alterations in Elp3 and Gcn5 are sufficient to confer severe phenotypes, the redundancy must be specifically related to the HAT activity of these co mplexes, In support of this conclusion, gcn5 Delta elp3 Delta phenotypes ar e suppressed by concomitant mutation of the HDA1 and HOS2 histone deacetyla ses, Our results demonstrate functional redundancy among transcription-asso ciated HAT and deacetylase activities, and indicate the importance of a fin e-tuned acetylation-deacetylation balance during transcription in vivo.