Interaction of recombinant Tetrahymena telomerase proteins p80 and p95 with telomerase RNA and telomeric DNA substrates.

Telomerase is a specialized reverse transcriptase that catalyzes telomeric repeat addition at the ends of existing telomeres or fragmented chromosomes. Two telomerase proteins from Tetrahymena thermophila, p80 and p95, were identified on the basis of their association with telomerase activity and telomerase RNA. Here we have produced recombinant versions of these proteins to characterize their functions in the ribonucleoprotein. Our findings indicate that the two proteins can form a complex whose association is independent of RNA. Each protein interacts directly with telomerase RNA, but the p80/p95 complex binds RNA with an affinity substantially greater than either protein alone. We have also characterized the DNA binding properties of p95 and show that it interacts with telomeric substrate DNAs with a specificity characteristic of the functionally defined Tetrahymena telomerase substrate anchor site. Together, these findings suggest a model in which protein-nucleic acid interactions separable from the active site contribute to positioning the template and primer, rather than exclusively the direct nucleic acid-active site interaction typical of other polymerases.