Figure 8. Working models for Ccq1‐mediated nucleosome stability and telomere maintenance.

1. Ccq1 recruits CLRC and SHREC to subtelomeric chromatin, which counteracts nucleosome instability conferred by the DNA sequence of TAS. CLRC may contribute to nucleosome stability indirectly by depositing H3K9me, which prevents access to RNAPII and, thus, nucleosome eviction through transcription. Conversely, stabilized nucleosomes will contribute to maintaining critical levels of H3K9me at TAS. SHREC may contribute to nucleosome stability directly through nucleosome positioning via its ATP‐dependent remodeler activity conferred by Mit1; indirectly through histone deacetylation via the HDAC moiety Clr3, thereby preventing open chromatin structure and access to RNAPII.
2. TAS or other DNA sequences may represent fragile sites causing DNA breaks through replication fork collapse or the recruitment of unknown factors causing genome instability. Ccq1 may prevent genomic instability by binding to subtelomeric chromatin, thereby stabilizing fragile sites and/or competing with the binding of destabilizing factors. Homologous sequences present in the TAS may promote recombination by BIR (break‐induced replication) or similar mechanisms.