The function of DNA polymerase alpha at telomeric g tails is important fortelomere homeostasis

Telomere length control is influenced by several factors, including telomer ase, the components of telomeric chromatin structure, and the conventional replication machinery, Although known components of the replication machine ry can influence telomere length equilibrium, little is known about why mut ations in certain replication proteins cause dramatic telomere lengthening. To investigate the cause of telomere elongation in cdc17/pol1 (DNA polymer ase alpha) mutants, we examined telomeric chromatin, as measured by its abi lity to repress transcription on telomere-proximal genes, and telomeric DNA end structures in pol1-17 mutants. pol1-17 mutants with elongated telomere s show a dramatic loss of the repression of telomere-proximal genes, or tel omeric silencing. In addition, cdc17/pol1 mutants grown under telomere-elon gating conditions exhibit significant increases in single-stranded characte r in telomeric DNA but not at internal sequences. The single strandedness i s manifested as a terminal extension of the G-rich strand (G tails) that ca n occur independently of telomerase, suggesting that cdc17/pol1 mutants exh ibit defects in telomeric lagging-strand synthesis. Interestingly, the loss of telomeric silencing and the increase in the sizes of the G tails at the telomeres temporally coincide and occur before any detectable telomere len gthening is observed. Moreover, the G tails observed in cdc17/pol1 mutants incubated at the semipermissive temperature appear only when the cells pass through S phase and are processed by the time cells reach G(1), These resu lts suggest that lagging-strand synthesis is coordinated with telomerase-me diated telomere maintenance to ensure proper telomere length control.