285: ESBX (Tb927.3.1660) integrates ESB RNA Pol I localization with BES activation and VSG repression in Trypanosoma brucei

Berazategui MA et al., Proc. Natl. Acad. Sci. U.S.A. 2026.123:e2531377123 - ESBX (Tb927.3.1660) links RNA Pol I localization at the ESB to activation of the active BES and repression of inactive BESs in Trypanosoma brucei, supporting monoallelic VSG expression. Key terms: Trypanosoma brucei, ESBX (Tb927.3.1660), expression site body, variant surface glycoprotein, RNA polymerase I. Study Highlights:Using ESB1-guided proximity-dependent biotinylation proteomics, endogenous tagging and high-resolution fluorescence microscopy, RNAi knockdown, RNA-seq, and inducible overexpression in bloodstream-form Trypanosoma brucei, the authors identify Tb927.3.1660 (ESBX) as an ESB-specific protein. ESBX localizes adjacent to Pol I (RPA2) and ESB1 within the ESB with measured center separations of ~68–175 nm and contains predicted SUMO-interacting and BRCT domains. ESBX depletion causes loss of the extranucleolar Pol I ESB focus, reduced processive transcription from the active BES with larger decreases distal to the promoter, and derepression of inactive BESs with low-processivity transcripts, whereas ESBX overexpression weakly activates inactive BESs with processive transcription without forming extra ESBs. Together the data indicate ESBX integrates activation of the active BES with repression of inactive BESs, a mechanism that supports monoallelic VSG expression. Conclusion:Tb927.3.1660/ESBX is an ESB component required to integrate activation of the active BES with repression of inactive BESs, thereby supporting monoallelic VSG expression in bloodstream-form Trypanosoma brucei. Music:Enjoy the music based on this article at the end of the episode. Article title:A factor integrating transcription and repression of surface antigen genes in African trypanosomes First author:Berazategui MA Journal:Proc. Natl. Acad. Sci. U.S.A. 2026.123:e2531377123 DOI:10.1073/pnas.2531377123 Reference:Berazategui MA, Wheeler RJ, Tiengwe C, Lansink LIM, Rudenko G, Sunter JD, Goodwin I, Gull K, Faria JRC, et al. A factor integrating transcription and repression of surface antigen genes in African trypanosomes. Proc. Natl. Acad. Sci. U.S.A. 2026.123:e2531377123. https://doi.org/10.1073/pnas.2531377123 License:This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) - https://creativecommons.org/licenses/by/4.0/ Support:Base by Base – Stripe donations: https://donate.stripe.com/7sY4gz71B2sN3RWac5gEg00 Official website https://basebybase.com On PaperCast Base by Base you’ll discover the latest in genomics, functional genomics, structural genomics, and proteomics. Episode link: https://basebybase.com/episodes/esbx-esb-vsg-regulation QC:This episode was checked against the original article PDF and publication metadata for the episode release published on 2026-02-09. QC Scope:- article metadata and core scientific claims from the narration- excludes analogies, intro/outro, and music- transcript coverage: Audited sections cover ESBX identification, ESB localization, functional knockdown and overexpression phenotypes, BRCT domain/phase separation discussion, transcriptional state model, and broader implications; not audited are full experimental methods or supplementary data in detail.- transcript topics: ESBX identification by proximity labeling and transcriptomics; ESBX localization to ESB near Pol I, ESB1, VEX2; ESBX depletion effects: growth arrest, ESB disassembly, active BES down, inactive BES derepression; ESBX overexpression effects: activation of inactive BESs, no extra ESBs; BRCT domains and phase separation notion for ESBX; Transcriptional state model: FE state, trickle state, enhanced trickle (ET) QC Summary:- factual score: 10/10- metadata score: 10/10