TELOMERASE CATALYTIC SUBUNIT HOMOLOGS FROM FISSION YEAST AND HUMAN

Catalytic protein subunits of telomerase from the ciliate Euplotes aed iculatus and the yeast Saccharomyces cerevisiae contain reverse transc riptase motifs. Here the homologous genes from the fission yeast Schiz osaccharomyces pombe and human are identified. Disruption of the S. po mbe gene resulted in telomere shortening and senescence, and expressio n of mRNA from the human gene correlated with telomerase activity in c ell lines. Sequence comparisons placed the telomerase proteins in the reverse transcriptase family but revealed hallmarks that distinguish t hem from retroviral and retrotransposon relatives. Thus, the proposed telomerase catalytic subunits are phylogenetically conserved and repre sent a deep branch in the evolution of reverse transcriptases.