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

13 páginas, 5 figuras, 1 tabla. Contiene información suplementaria en: Supplementary information accompanies this paper at https://doi.org/10.1186/s13072-020-00367-3Background: Histone H2B deubiquitination is performed by numerous deubiquitinases in eukaryotic cells including Ubp8, the catalytic subunit of the tetrameric deubiquitination module (DUBm: Ubp8; Sus1; Sgf11; Sgf73) of the Spt-Ada-Gcn5 acetyltransferase (SAGA). Ubp8 is linked to the rest of SAGA through Sgf73 and is activated by the adaptors Sus1 and Sgf11. It is unknown if DUBm/Ubp8 might also work in a SAGA-independent manner. Results: Here we report that a tetrameric DUBm is assembled independently of the SAGA-CORE components SPT7, ADA1 and SPT20. In the absence of SPT7, i.e., independent of the SAGA complex, Ubp8 and Sus1 are poorly recruited to SAGA-dependent genes and to chromatin. Notably, cells lacking Spt7 or Ada1, but not Spt20, show lower levels of nuclear Ubp8 than wild-type cells, suggesting a possible role for SAGA-CORE subunits in Ubp8 localization. Last, deletion of SPT7 leads to defects in Ubp8 deubiquitinase activity in in vivo and in vitro assays. Conclusions: Collectively, our studies show that the DUBm tetrameric structure can form without a complete intact SAGA-CORE complex and that it includes full-length Sgf73. However, subunits of this SAGA-CORE influence DUBm association with chromatin, its localization and its activity.This study was supported by funds to SR-N from the Spanish MINECO, MICIIN (BFU2014-57636, BFU2015-71978, PGC2018-099872-B-I00) and the Generalitat Valenciana (PROM/2012/061, ACOMP2014/061 and PROMETEO 2016/093). This work was supported by FEDER 2014–2020 and the Ministerio de Economia y Competitividad (MINECO) of Spain. V.G-M was supported by the FPU program from the Ministerio de Educación y Ciencia (AP2009-0917); C.C-N by the Generailtat Valenciana PROMETEO/2016/093; P.O-C by the FPI program from MINECO (BES2012-058587); and M.M-E by the GVA (Val I+D: ACIF/2015/025). The M.I-V lab was co-funded by European Regional Development Funds (ERDF) and the Horizon 2020 Framework Programme of the European Union under the grant agreement 688945 (Euro-BioImaging Prep Phase II).Peer reviewe

G4access identifies G-quadruplexes and their associations with open chromatin and imprinting control regions

International audienceMetazoan promoters are enriched in secondary DNA structure-forming motifs, such as G-quadruplexes (G4s). Here we describe ‘G4access’, an approach to isolate and sequence G4s associated with open chromatin via nuclease digestion. G4access is antibody- and crosslinking-independent and enriches for computationally predicted G4s (pG4s), most of which are confirmed in vitro. Using G4access in human and mouse cells, we identify cell-type-specific G4 enrichment correlated with nucleosome exclusion and promoter transcription. G4access allows measurement of variations in G4 repertoire usage following G4 ligand treatment, HDAC and G4 helicases inhibitors. Applying G4access to cells from reciprocal hybrid mouse crosses suggests a role for G4s in the control of active imprinting regions. Consistently, we also observed that G4access peaks are unmethylated, while methylation at pG4s correlates with nucleosome repositioning on DNA. Overall, our study provides a new tool for studying G4s in cellular dynamics and highlights their association with open chromatin, transcription and their antagonism to DNA methylation

G-quadruplexes are promoter elements controlling nucleosome exclusion and RNA polymerase II pausing

Despite their central role in transcription, it has been difficult to define universal sequences associated to eukaryotic promoters. Within chromatin context, recruitment of the transcriptional machinery requires opening of the promoter but how DNA elements could contribute to this process has remained elusive. Here, we show that G-quadruplex (G4) secondary structures are highly enriched mammalian core promoter elements. G4s are located at the deepest point of nucleosome exclusion at promoters and correlate with maximum promoter activity. We found that experimental G4s exclude nucleosomes both in vivo and in vitro and display a strong positioning potential. At model promoters, impairing G4s affected both transcriptional activity and chromatin opening. G4 destabilization also resulted in an inactive promoter state and affected transition to effective RNA production in live imaging experiments. Finally, G4 stabilization resulted in global reduction of proximal promoter pausing. Altogether, our data introduce G4s as bona fide promoter elements allowing nucleosome exclusion and facilitating pause release by the RNA Polymerase II