Latent effects of Hsp90 mutants revealed at reduced expression levels

PLoS Genet. 2013 Jun;9(6):e1003600. doi: 10.1371/journal.pgen.1003600. Epub 2013 Jun 27.


In natural systems, selection acts on both protein sequence and expression level, but it is unclear how selection integrates over these two dimensions. We recently developed the EMPIRIC approach to systematically determine the fitness effects of all possible point mutants for important regions of essential genes in yeast. Here, we systematically investigated the fitness effects of point mutations in a putative substrate binding loop of yeast Hsp90 (Hsp82) over a broad range of expression strengths. Negative epistasis between reduced expression strength and amino acid substitutions was common, and the endogenous expression strength frequently obscured mutant defects. By analyzing fitness effects at varied expression strengths, we were able to uncover all mutant effects on function. The majority of mutants caused partial functional defects, consistent with this region of Hsp90 contributing to a mutation sensitive and critical process. These results demonstrate that important functional regions of proteins can tolerate mutational defects without experimentally observable impacts on fitness.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acid Substitution / genetics
  • Gene Expression Regulation, Fungal
  • Genetic Fitness*
  • HSP90 Heat-Shock Proteins / genetics*
  • Mutation
  • Point Mutation / genetics
  • Saccharomyces cerevisiae / genetics*
  • Saccharomyces cerevisiae Proteins / genetics*
  • Selection, Genetic / genetics*
  • Substrate Specificity


  • HSP82 protein, S cerevisiae
  • HSP90 Heat-Shock Proteins
  • Saccharomyces cerevisiae Proteins