Characterization of a metazoan ADA acetyltransferase complex

Abstract

The Gcn5 acetyltransferase functions in multiple acetyltransferase complexes in yeast and metazoans. Yeast Gcn5 is part of the large SAGA (Spt-Ada-Gcn5 acetyltransferase) complex and a smaller ADA acetyltransferase complex. In flies and mammals, Gcn5 (and its homolog pCAF) is part of various versions of the SAGA complex and another large acetyltransferase complex, ATAC (Ada2A containing acetyltransferase complex). However, a complex analogous to the small ADA complex in yeast has never been described in metazoans. Previous studies in Drosophila hinted at the existence of a small complex which contains Ada2b, a partner of Gcn5 in the SAGA complex. Here we have purified and characterized the composition of this complex and show that it is composed of Gcn5, Ada2b, Ada3 and Sgf29. Hence, we have named it the metazoan ‘ADA complex’. We demonstrate that the fly ADA complex has histone acetylation activity on histones and nucleosome substrates. Moreover, ChIP-Sequencing experiments identified Ada2b peaks that overlap with another SAGA subunit, Spt3, as well as Ada2b peaks that do not overlap with Spt3 suggesting that the ADA complex binds chromosomal sites independent of the larger SAGA complex.

SAGA–CORE subunit Spt7 is required for correct Ubp8 localization, chromatin association and deubiquitinase activity

“…In the absence of SPT7 , the pair of Spt7–Taf10 would not form, which would prevent SAGA association with the histone octamer leading to poor access of Ubp8 to nucleosomal H2Bub1. The newly reported cryo-EM structure of the SAGA nucleosome complex shows that the DUBm is displaced from the SAGA–CORE in a chromatin-bound state [ 18 , 42 ]. The flexibility of the SAGA complex and the presence of different interconnected submodules allow SAGA to modify different histones substrates in a regulated manner.…”

Unique roles of ATAC and SAGA - KAT2A complexes in normal and malignant hematopoiesis

“…S5C), including members of the Core, but also the SAGA-specific HAT subunit TADA2B and the H2B de-ubiquitinase USP22 (Supplemental File 4). SAGA HAT can exist as a separate complex, at least in Drosophila (Soffers et al 2019), which may explain some level of independence from the Core. On the other hand, the recent elucidation of the structure of yeast SAGA (Papai et al 2020;Wang et al 2020) suggests that DUB nucleosome binding is an early event in complex reconfiguration leading to activation of transcription.…”

“…Altogether, the data are compatible with a requirement for SAGA-dependent enzymatic activities on erythroid differentiation post-commitment, which may not be strictly dependent on the association with the Core. This could be because one or both enzymatic modules may exist and interact as independent complexes in at least some cell types (Soffers et al 2019). Alternatively, the presence of residual SPT20 transcript upon knockdown, rather than knockout, of SUPT20H expression, may also allow for sufficient basal SAGA assembly.…”

SAGA-CORE subunit Spt7 is required for correct Ubp8 localization, chromatin association and deubiquitinase activity

“…In the absence of SPT7, the pair of Spt7-Taf10 would not form, which would prevent SAGA association with the histone octamer leading to poor access of Ubp8 to nucleosomal H2Bub1. The newly reported cryo-EM structure of the SAGA nucleosome complex shows that the DUBm is displaced from the SAGA-CORE in a chromatin-bound state [18,42]. The exibility of the SAGA complex and the presence of different interconnected submodules allow SAGA to modify different histones substrates in a regulated manner.…”