Transcribing Centromeres: Noncoding RNAs and Kinetochore Assembly

Chromosome segregation depends on the attachment of spindle microtubules to sites on chromosomal DNA known as centromeres, through kinetochore protein complexes. Although RNA was found in kinetochores in the 1970s, only with recent investigations has evidence emerged that loading of the centromere-specific nucleosomes that form the foundation of the kinetochore may be coupled to centromeric transcription. Centromeric transcripts are bound by several kinetochore proteins that require them for stabilization or localization. At least some centromeres have promoter activity, and many have non-B form DNA that may facilitate their transcription. Whereas other noncoding RNAs regulate gene expression or silence transposons, cotranscriptional assembly of kinetochores is a novel function for noncoding RNAs. Centromeres are transcribed at a low level and transcripts are incorporated into centromeric chromatin, where they serve essential functions. Several kinetochore proteins bind centromeric transcripts, which may be necessary to stabilize or localize the proteins. Loading of centromere-specific nucleosomes may be coupled to centromeric transcription. Some centromeres have known promoter activity and most centromeres are enriched in non-B form DNA that may facilitate transcription or loading of centromere-specific nucleosomes.