A Naturally Thermolabile Activity Compromises Genetic Analysis of Telomere Function in Saccharomyces cerevisiae.

The core assumption driving the use of conditional loss-of-function reagents such as temperature-sensitive mutations is that the resulting phenotype(s) are solely due to depletion of the mutant protein under non-permissive conditions. However, prior published data, combined with observations presented here, challenge the generality of this assumption at least for telomere ...
biology: for both wild type yeast and strains bearing null mutations in telomere protein complexes, there is an additional phenotypic consequence when cells are grown above 34°. We propose that this synthetic phenotype is due to a naturally thermolabile activity that confers a telomere-specific defect, which we call the Tmp(-) phenotype. This prompted a re-examination of commonly used cdc13-ts and stn1-ts mutations, which indicates that these alleles are instead hypomorphic mutations that behave as apparent temperature-sensitive mutations due to the additive effects of the Tmp(-) phenotype. We therefore generated new cdc13-ts reagents which are non-permissive below 34° to allow examination of cdc13-depleted phenotypes in the absence of this temperature-dependent defect. A return-to-viability experiment following prolonged incubation at 32°, 34° and 36° with one of these new cdc13-ts alleles argues that the accelerated inviability previously observed at 36° in cdc13-1 rad9- mutant strains is a consequence of the Tmp(-) phenotype. Although this study focused on telomere biology, viable null mutations which confer inviability at 36° have been identified for multiple cellular pathways. Thus, phenotypic analysis of other aspects of yeast biology may similarly be compromised at high temperatures by pathway-specific versions of the Tmp(-) phenotype.
Date: Feb. 29, 2012
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