Altering telomere structure allows telomerase to act in yeast lacking ATM kinases.
BACKGROUND
Telomerase is a ribonucleoprotein that copies a short RNA template into telomeric DNA, maintaining eukaryotic chromosome ends and preventing replicative senescence. Telomeres differentiate chromosome ends from DNA double-stranded breaks. Nevertheless, the DNA damage-responsive ATM kinases Tel1p and Mec1p are required for normal telomere maintenance in Saccharomyces cerevisiae. We tested whether the ATM kinases are required for telomerase enzyme activity or whether it is their action on the telomere that allows telomeric DNA synthesis.


RESULTS
Cells lacking Tel1p and Mec1p had wild-type levels of telomerase activity in vitro. Furthermore, altering telomere structure in three different ways showed that telomerase can function in ATM kinase-deleted cells: tel1 mec1 cells senesced more slowly than tel1 mec1 cells that also lacked TLC1, which encodes telomerase RNA, suggesting that tel1 mec1 cells have residual telomerase function; deleting the telomere-associated proteins Rif1p and Rif2p in tel1 mec1 cells prevented senescence; we isolated a point mutation in the telomerase RNA template domain (tlc1-476A) that altered telomeric DNA sequences, causing uncontrolled telomeric DNA elongation and increasing single strandedness. In tel1 mec1 cells, tlc1-476A telomerase was also capable of uncontrolled synthesis, but only after telomeres had shortened for >30 generations.


CONCLUSIONS
Our results show that, without Tel1p and Mec1p, telomerase is still active and can act in vivo when the telomere structure is disrupted by various means. Hence, a primary function of the ATM-family kinases in telomere maintenance is to act on the substrate of telomerase, the telomere, rather than to activate the enzymatic activity of telomerase.
Chan
S W
SW
Department of Biochemistry and Biophysics, University of California-San Francisco, San Francisco, CA 94143, USA.
Chang
J
J
Prescott
J
J
Blackburn
E H
EH
D064007:Ataxia Telangiectasia Mutated Proteins; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins; D019098:Telomerase / Q000378:metabolism*; D016615:Telomere / Q000737:chemistry / Q000378:metabolism*; D034501:Telomere-Binding Proteins; D025521:Tumor Suppressor Proteins
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D047908:Intracellular Signaling Peptides and Proteins; C105362:RIF2 protein, S cerevisiae; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D034501:Telomere-Binding Proteins; D025521:Tumor Suppressor Proteins; C074461:RIF1 protein, S cerevisiae; D064007:Ataxia Telangiectasia Mutated Proteins; C088937:MEC1 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; C513623:TEL1 protein, S cerevisiae; D019098:Telomerase