The role of SAGA coactivator complex in snRNA transcription

Abstract

The general snRNA gene transcription apparatus has been extensively studied. However, the role of coactivators in this process is far from being clearly understood. Here, we have demonstrated that the Drosophila SAGA complex interacts with the PBP complex, the key component of the snRNA gene transcription apparatus, and is present at the promoter regions of the snRNA genes transcribed by both the RNA polymerase II and RNA polymerase III (U6 snRNA). We show that SAGA interacts with the Brf1 transcription factor, which is a part of the RNA polymerase III transcription apparatus and is present at promoters of a number of Pol III-transcribed genes. Mutations inactivating several SAGA subunit genes resulted in reduced snRNA levels in adult flies, indicating that SAGA is indeed the transcriptional coactivator for the snRNA genes. The transcription of the Pol II and Pol III-transcribed U genes was reduced by mutations in all tested SAGA complex subunits. Therefore, the transcription of the Pol II and Pol III-transcribed U genes was reduced by the mutations in the deubiquitinase module, as well as in the acetyltransferase module of the SAGA, indicating that the whole complex is essential for their transcription. Therefore, the SAGA complex activates snRNA genes suggesting its wide involvement in the regulation of gene transcription, and consequently, in the maintenance of cellular homeostasis.

The role of SAGA in the transcription and export of mRNA

“…Our results are in agreement with the data that the DUB module has both SAGA-related and independent functions. In summary, it can be argued that the SAGA complex in metazoans is widely involved in the regulation of gene transcription (Popova et al, 2018).…”

The SAGA Deubiquitinilation (DUB) Module Participates in Pol III-Dependent Transcription

“…Antibodies to Sgf11, ENY2, and Gcn5, available in our laboratory, were used in chromatin immunoprecipitation reactions. Since it was previously shown that the SAGA and DUB module are present on the promoters of both Pol II and Pol III dependent genes, we assessed the presence of factors on the promoter of the hsp70 gene (Pol IIdependent gene) in heat shock and on Pol III targets, the presence of SAGA in which has been shown previously [18,35].…”

“…Recently, SAGA was found to be involved in the transcription of small nuclear RNA (snRNA) genes in both Pol II-and Pol III-dependent [18]. Pol III transcribes a set of noncoding RNAs, including tRNA, 5S RNA, and U6 snRNA [19].…”

“…Antibodies. We used polyclonal antibodies to proteins Sgf11, ENY2, Gcn5, Brf1, Pbp45, obtained earlier in our laboratory [17,18,30,31].…”

SAGA and SAGA-like SLIK transcriptional coactivators are structurally and biochemically equivalent

“…SAGA-mediated chromatin modifications are important for expression of nearly all genes ( 5 , 6 ). The role of SAGA extends beyond transcription and includes mRNA export ( 7 , 8 ), mRNA splicing ( 8 ), RNA polymerase II- and III-dependent snRNA transcription ( 9 ), and DNA repair ( 10 , 11 ). SAGA is also important for development in metazoans ( 12 ) and tolerance of plants to environmental stress ( 13 ).…”