Immortalized cell lines maintain telomeres by the expression of telomerase or by a mechanism designated alternative lengthening of telomeres (ALT). Although DNA polymerase α (pol-α) is reported to be required for telomere maintenance, the critical role of pol-α in telomere maintenance has not been firmly determined. We examined the role of retinoblastoma protein (pRb) and pol-α in the regulation of telomere length, using telomere-fiber FISH. Telomere length varied dependent on the intracellular abundance of pol-α or pRb in HeLa cells. A proportion of hyper-phosphorylated pRb (ppRb) molecules localized to sites of telomeric DNA replication in HeLa cells. Pol-α might thus contribute to telomere maintenance, and might be regulated by ppRb.
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