Eukaryotic genome integrity is safeguarded by two highly conserved protein kinases that are called ATR and ATM in humans and Mec1 and Tel1 in S. cerevisiae. Although they share sequence similarities and substrates, these protein kinases perform different specialized functions. In particular, Mec1 plays a key role in the DNA damage checkpoint response, whereas Tel1 is primarily involved in telomere homeostasis and its checkpoint function is masked by the prevailing activity of Mec1. In order to understand how this specificity is achieved, we searched for TEL1 mutations able to compensate for the lack of Mec1 functions. Here, we describe seven independent dominant TEL1hy alleles that are able to suppress to different extents both the hypersensitivity to genotoxic agents and the checkpoint defects of Mec1-deficient cells. Most of these alleles also cause telomere overelongation. In vitro kinase activity was increased compared to wild type Tel1 in the Tel1hy-385, Tel1hy-394, Tel1hy-680 and Tel1hy-909 variants, but it was not affected by the TEL1hy-184 and TEL1hy-628 mutations and it was slightly reduced by the TEL1hy-544 mutation. Thus, the phenotypes caused by at least some Tel1hy variants are not simply the consequence of improved catalytic activity. Further characterization shows that Tel1hy-909 not only can sense and signal a single DSB, unlike wild type Tel1, but also contributes more efficiently than Tel1 to single-stranded DNA accumulation at double-strand ends, thus enhancing Mec1 signalling activity. Moreover, it causes unscheduled checkpoint activation during unperturbed conditions and upregulates the checkpoint response to low amounts of DNA lesions. Finally, Tel1hy-544 can activate the checkpoint more efficiently than wild type Tel1, while it causes telomere shortening, indicating that the checkpoint and telomeric functions of Tel1 can be separable.
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|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Phenotype||Experiment Type||Experiment Type Category||Mutant Information||Strain Background||Chemical||Details||Reference|
|Evidence ID||Analyze ID||Regulator||Regulator Systematic Name||Target||Target Systematic Name||Experiment||Assay||Construct||Conditions||Strain Background||Reference|