Functional requirement of p23 and Hsp90 in telomerase complexes

Most normal human diploid cells have no detectable telomerase; however, exp ression of the catalytic subunit of telomerase is sufficient to induce telo merase activity and, in many cases, will bypass normal senescence. We and o thers have previously demonstrated in vitro assembly of active telomerase b y combining the purified RNA component with the reverse transcriptase catal ytic component synthesized in rabbit reticulocyte extract. Here rye show th at assembly of active telomerase from in vitro-synthesized components requi res the contribution of proteins present in reticulocyte extracts. We have identified the molecular chaperones p23 and Hsp90 as proteins that bind to the catalytic subunit of telomerase. Blockade of this interaction inhibits assembly of active telomerase in vitro. Also, a significant fraction of act ive telomerase from cell extracts is associated with p23 and Hsp90. Consist ent with in vitro results, inhibition of Hsp90 function in cells blocks ass embly of active telomerase. To our knowledge, p23 and Hsp90 are the first t elomerase-associated proteins demonstrated to contribute to telomerase acti vity.