Yeast telomerase is specialized for C/A-rich RNA templates.
Telomeres, the protective caps of eukaryotic chromosomes, are maintained by the enzyme telomerase. This telomere-specific reverse transcriptase (RT) uses a small region of its RNA subunit as template to synthesize telomeric DNA, which is generally G/T rich in the strand that contains the 3' end. To further our understanding of why telomeres are usually G/T rich, we screened Saccharomyces cerevisiae telomerase RNA (TLC1) libraries with randomized template sequences for complementation of a tlc1 deletion and decapping of existing telomeres. Surprisingly, the vast majority of the 60 000 different mutant telomerase templates tested showed no activity in vivo. This deficiency was not due to impaired assembly with the catalytic subunit (Est2p) nor could it be alleviated by enforced telomerase recruitment to the telomeres. Rather, the mutant templates reduced the nucleotide addition processivity of telomerase. The functional RNA template sequences recovered in our screens preferentially contained two or more consecutive rC nucleotides, reminiscent of the wild-type template. Thus, in contrast to retroviral RTs that can reverse transcribe any RNA sequence into DNA, the budding yeast telomerase RT is specialized for its C-rich RNA template.
Förstemann
Klaus
K
Swiss Institute for Experimental Cancer Research (ISREC), Chemin des Boveresses 155, CH-1066 Epalinges, Switzerland.
Zaug
Arthur J
AJ
Cech
Thomas R
TR
Lingner
Joachim
J
D000225:Adenine / Q000378:metabolism; D001483:Base Sequence; D003596:Cytosine / Q000378:metabolism; D005816:Genetic Complementation Test; D009154:Mutation; D011485:Protein Binding; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D013379:Substrate Specificity; D019098:Telomerase / Q000235:genetics / Q000378:metabolism*; D016615:Telomere / Q000235:genetics / Q000378:metabolism
D012331:RNA, Fungal; D003596:Cytosine; D019098:Telomerase; D000225:Adenine