A transcriptional roadblock protects yeast centromeres

Centromeres are the chromosomal loci essential for faithful chromosome segregation during cell division. Although centromeres are transcribed and produce non-coding RNAs (cenRNAs) that affect centromere function, we still lack a mechanistic understanding of how centromere transcription is regulated. Here, using a targeted RNA isoform sequencing approach, we identified the transcriptional landscape at and surrounding all centromeres in budding yeast. Overall, cenRNAs are derived from transcription readthrough of pericentromeric regions but rarely span the entire centromere and are a complex mixture of molecules that are heterogeneous in abundance, orientation, and sequence. While most pericentromeres are transcribed throughout the cell cycle, centromere accessibility to the transcription machinery is restricted to S-phase. This temporal restriction is dependent on Cbf1, a centromere-binding transcription factor, that we demonstrate acts locally as a transcriptional roadblock. Cbf1 deletion leads to an accumulation of cenRNAs at all phases of the cell cycle which correlates with increased chromosome mis-segregation that is partially rescued when the roadblock activity is restored. We propose that a Cbf1-mediated transcriptional roadblock protects yeast centromeres from untimely transcription to ensure genomic stability.