The Drosophila Histone Acetyltransferase Gcn5 and Transcriptional Adaptor Ada2a Are Involved in Nucleosomal Histone H4 Acetylation

Abstract

The histone acetyltransferase (HAT) Gcn5 plays a role in chromatin structure and gene expression regulation as a catalytic component of multiprotein complexes, some of which also contain Ada2-type transcriptional coactivators. Data obtained mostly from studies on yeast (Saccharomyces cerevisiae) suggest that Ada2 potentiates Gcn5 activity and substrate recognition. dAda2b, one of two related Ada2 proteins of Drosophila melanogaster, was recently found to play a role in complexes acetylating histone 3 (H3). Evidence of an in vivo functional link between the related coactivator dAda2a and dGcn5, however, is lacking. Here we present data on the genetic interaction of dGcn5 and dAda2a. The loss of either dGcn5 or dAda2a function results in similar chromosome structural and developmental defects. In dAda2a mutants, the nucleosomal H4 acetylation at lysines 12 and 5 is significantly reduced, while the acetylation established by dAda2b-containing Gcn5 complexes at H3 lysines 9 and 14 is unaffected. The data presented here, together with our earlier data on the function of dAda2b, provide evidence that related Ada2 proteins of Drosophila, together with Gcn5 HAT, are involved in the acetylation of specific lysine residues in the N-terminal tails of nucleosomal H3 and H4. Our data suggest dAda2a involvement in both uniformly distributed H4 acetylation and gene-specific transcription regulation.

We thank KatalinÖ krös for her expert technical help. We are grateful to Cristophe Antoniewsky and László Tora for kindly providing dGcn5^C137T, dGcn5^E333st stocks and Gcn5 ΔPcafΔ Ada ΔHat transgenes and Pol II antibody, respectively, and for critical comments and discussion of the results prior to publication. We thank IstvánTombácz and Norbert Pardi for their contribution to the selection of dGcn5 mutants and ZsuzsannaÚ jfaludi for her help with Q-PCR. SelenMuratoglu and Zsolt Tóth participated in the early phase of these studies. We are grateful for their contribution. We are very grateful to L. Lebedeva for her help with polytene chromosome immunostaining.

This work was supported by grants from the Hungarian Science Fund (OTKA T046414) and EU FP-6 (LSHG-CT-2004-502950). A.C. is a European Community RTN Marie Curie research fellow, supported by grant HPRN-CT-2004-504228.