Project description:Chromatin proteins competes with the transcription machinery for access to genomic DNA and suppress cryptic promoters. CRISPR arrays form the physical memory of CRISPR adaptive immune systems. The incorporation of virus-derived AT-rich DNA into CRISPR arrays renders them prone to harbouring cryptic promoters. Sulfolobales feature extremely long CRISPR arrays spanning several kilobases as well as a CRISPR-specific chromatin protein termed Cbp1. Altered Cbp1 expression affects transcription from CRISPR arrays in multiple ways, but the mechanistic basis remains to be understood. Here, we show that Cbp1 recruits the general chromatin protein Cren7 to form a heteromeric chromatin complex at CRISPR arrays. Cbp1-CreN7 chromatinisation plays a dual role in the transcription of CRISPR array. It suppresses spurious transcription from cryptic CRISPR array-internal promoters via steric occlusion of the transcription machinery while enhancing transcription from promoters in the CRISPR leaders. Our results show that Cbp1-CreN7 chromatinization drives the coordinated transcription of long CRISPR arrays. Additional binding sites of Cbp1 associated with transposases and the leaders of alternative CRISPR arrays hint on a wider regulatory function of Cbp1 linking defense systems and mobile genetic elements.
Project description:Chromatin proteins competes with the transcription machinery for access to genomic DNA and suppress cryptic promoters. CRISPR arrays form the physical memory of CRISPR adaptive immune systems. The incorporation of virus-derived AT-rich DNA into CRISPR arrays renders them prone to harbouring cryptic promoters. Sulfolobales feature extremely long CRISPR arrays spanning several kilobases as well as a CRISPR-specific chromatin protein termed Cbp1. Altered Cbp1 expression affects transcription from CRISPR arrays in multiple ways, but the mechanistic basis remains to be understood. Here, we show that Cbp1 recruits the general chromatin protein Cren7 to form a heteromeric chromatin complex at CRISPR arrays. Cbp1-CreN7 chromatinisation plays a dual role in the transcription of CRISPR array. It suppresses spurious transcription from cryptic CRISPR array-internal promoters via steric occlusion of the transcription machinery while enhancing transcription from promoters in the CRISPR leaders. Our results show that Cbp1-CreN7 chromatinization drives the coordinated transcription of long CRISPR arrays. Additional binding sites of Cbp1 associated with transposases and the leaders of alternative CRISPR arrays hint on a wider regulatory function of Cbp1 linking defense systems and mobile genetic elements.
