Functional multimerization of the human telomerase reverse transcriptase

The telomerase enzyme exists as a large complex (similar to1,000 kDa) in ma mmals and at minimum is composed of the telomerase RNA and the catalytic su bunit telomerase reverse transcriptase (TERT). In Saccharomyces cerevisiae, telomerase appears to function as an interdependent dimer or multimer in v ivo (J. Prescott and E. H. Blackburn, Genes Dev. 11:2790-2800, 1997). Howev er, the requirements for multimerization are not known, and it remained unc lear whether telomerase exists as a multimer in other organisms. We show he re that human TERT (hTERT) forms a functional multimer in a rabbit reticulo cyte lysate reconstitution assay and in human cell extracts. Two separate, catalytically inactive TERT proteins can complement each other in trans to reconstitute catalytic activity. This complementation requires the amino te rminus of one hTERT and the reverse transcriptase and C-terminal domains of the second hTERT. The telomerase RNA must associate with only the latter h TERT for reconstitution of telomerase activity to occur. Multimerization of telomerase also facilitates the recognition and elongation of substrates i n vitro and in vivo. These data suggest that the catalytic core of human te lomerase may exist as a functionally cooperative dimer or multimer in vivo.