Cdc13

Cdc13 is a telomere-binding protein in the budding yeast Saccharomyces cerevisiae. It specifically associates with the single-stranded G-rich telomeric DNA at chromosome ends and is a central component of the CST complex, which also includes Stn1 and Ten1. Through its DNA- and protein-binding activities, Cdc13 helps cap telomeres and protect them from degradation and erroneous checkpoint activation.

Cdc13 plays multiple roles in telomere maintenance. It regulates telomerase access to telomeres by recruiting the Est1 subunit, thereby influencing telomere elongation. It also participates in coordinating late-stage telomere replication, including C-strand synthesis, by acting in concert with replication factors such as DNA polymerase alpha-primase. In this way, Cdc13 contributes to telomere length homeostasis and genome stability.

Regulation and interactions are integral to Cdc13 function. The protein interacts with Stn1 and Ten1 to form the CST complex, and it engages with telomerase components to modulate extension events. Its activity is subject to cell cycle–dependent regulation and DNA damage signaling, ensuring telomere protection is coordinated with replication and repair pathways.

Genetic mutations of CDC13 can lead to telomere uncapping and genome instability. The cdc13-1 allele, for example, exhibits temperature-sensitive defects in telomere protection, resulting in activation of DNA damage responses and growth defects at restrictive temperatures. The CST complex is conserved across eukaryotes, and in many organisms the vertebrate homologs (CTC1-STN1-TEN1) perform analogous roles in telomere protection and replication.

Cdc13 was identified in yeast genetic screens for telomere maintenance and has since been a key model for understanding telomere biology and CST-mediated telomere regulation.