Dbp7 and RNA exosome subunit Dis3 interacts to mediate CENP-A loading via CENP-A chaperone Sim3

Background: Centromeres are crucial for proper chromosomes segregation during cell division. Centromeres in most eukaryotes are epigenetically specified by the histone 3 (H3) variant, CENP-A. How CENP-A precisely targets to centromeres remains elusive. Centromeres are typically transcribed into non-coding RNAs, which have been implicated in centromere functions. But the exact role of centromeric RNA in CENP-A loading is still poorly understood. In addition, centromere transcription induce formation of R-loops consisting of a DNA:RNA hybrid and a displaced single-stranded DNA. Excessive R-loops lead to genome instability. Little is known about the mechanism used for safeguarding centromeres against R-loops. Results: Here we show that through a visual genetic screen, we identified a conserved RNA binding protein Dbp7 that plays a critical role in CENP-A loading to centromeres. Deletion of dbp7+ results in CENP-A mislocalization and defects in chromosome segregation and centromere silencing. We found that Dbp7 associates with centromere transcripts, and further showed that Dbp7 prevents accumulation of R-loops at centromeres. Our domain-deletion analysis demonstrated that the DEAD-box helicase domain and the C-terminal extension motif of Dbp7 contribute to its role in centromere function. In addition, Dbp7 interacts with the key exosome subunit Dis3. Importantly, we found that Dis3 promotes CENP-A centromere loading by interacting the CENP-A chaperone Sim3. Conclusions: Together, this study uncovered a previously unrecognized CENP-A loading mechanism, by which Dbp7 and Dis3 bind to centromeric transcripts and in turn mediate recruitment of CENP-A via recruiting Sim3. Our work also provides mechanistic insight into R-loop resolution at centromeres. We analyzed dbp7Δ mutant cells and wild type carrying Cnp1-GFP by ChIP followed by high-throughput sequencing (ChIP-seq) to detect the distribution of Cnp1 in the two strains.