Cell-cycle-dependent regulation of telomere binding proteins: roles of Polo-like kinase.
The telomere is a functional complex at chromosomal termini consisting of repetitive DNA and associated proteins, and protects the ends against degradation and fusion. Telomeric repeat binding factors TRF1 and TRF2 bind directly to double-stranded telomeric DNA. Although structurally related, TRF1 and TRF2 contribute to telomere maintenance in distinct ways: TRF1 negatively regulates telomerase-dependent telomere lengthening, whereas TRF2 plays an important role in protecting chromosomal ends. It is not known how the proteinaceous complex manages DNA metabolism such as DNA replication, which requires the recruitment of numerous trans-acting factors. We have found that Xenopus TRF1 (xTRF1) specifically associates with mitotic chromatin and dissociates from interphase replicating chromatin. In contrast, Xenopus TRF2 (xTRF2) binds to telomeric DNA throughout the cell cycle. Interestingly, telomerase activity is associated with the interphase chromatin, but not with the mitotic chromatin. These results support a model in which telomeres form a semi-open configuration that allows access of telomerase and replication machineries, yet protects the chromosomal ends in S phase. Interestingly, M phase specific telomere binding of xTRF1 requires Polo-like kinase, a key regulator of mitosis. We discuss the relevance of our studies and recent findings of other groups to indicate the possible role of Polo-like kinase in telomere regulation.
Nishiyama
Atsuya
A
Laboratory of Cell Cycle Regulation, Department of Gene Mechanisms, Graduate School of Biostudies, Kyoto University, Kyoto, Japan.
Ishikawa
Fuyuki
F
D000818:Animals; D002453:Cell Cycle; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D006801:Humans; D011485:Protein Binding; D019098:Telomerase / Q000378:metabolism; D034501:Telomere-Binding Proteins / Q000235:genetics / Q000378:metabolism*
D002843:Chromatin; D034501:Telomere-Binding Proteins; D019098:Telomerase