A fission yeast CENP-B homolog Abp1 prevents RNAi-mediated heterochromatin formation at ribosomal DNA repeats.

The article focuses on the role of the CENP-B homolog Abp1 in regulating facultative heterochromatin formation at ribosomal DNA (rDNA) repeats in the fission yeast *Schizosaccharomyces pombe* under glucose starvation. It demonstrates that Abp1 is essential for proper recruitment of RNA polymerase I (RNAPI) and rRNA expression during vegetative growth, while its loss leads to increased nucleosome occupancy, ectopic RNA polymerase II (RNAPII) transcription, and excessive RNA interference (RNAi)-dependent heterochromatin marked by histone H3 lysine 9 methylation (H3K9me) at rDNA repeats. Under glucose starvation, Abp1 partially dissociates from rDNA, facilitating controlled heterochromatinization necessary for cellular adaptation, but excessive heterochromatin in abp1Δ mutants impairs exit from quiescence despite not affecting viability. These findings suggest that Abp1 modulates a balance between transcriptional activity and heterochromatin assembly at rDNA to regulate ribosomal RNA production and cellular responses to nutritional stress.