Temperature-sensitive mutant

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Temperature sensitive mutants are variants of genes that allow normal function of the organism at low temperatures, but altered function at higher temperatures.


Most temperature sensitive mutations affect proteins, and cause loss of protein function at the non-permissive temperature. The permissive temperature is one at which the protein typically can fold properly, or remain properly folded. At higher temperatures, the protein is unstable and ceases to function properly. These mutations are usually recessive in diploid organisms.

Permissive temperature[edit]

The permissive temperature is the temperature at which a temperature sensitive mutant gene product takes on a normal, functional phenotype.[1] When a temperature sensitive mutant is grown in a permissive condition, the mutated gene product behaves normally (meaning that the phenotype isn't observed), even if there is a mutant allele present. This results in the survival of the cell or organism, as if it were a wild type strain. In contrast, the nonpermissive temperature or restrictive temperature is the temperature at which the mutant phenotype is observed.

Use in Research[edit]

Temperature sensitive mutants are useful in biological research. They allow to study essential processes required for the survival of the cell or organism. Mutations to essential genes are generally lethal and hence temperature sensitive mutants enable researchers to induce the phenotype at the restrictive temperatures and study the effects. The temperature sensitive phenotype could be expressed during a specific developmental stage to study the effects.


Temperature sensitive mutants were used by Randy Schekman's group to isolate and identify mutants having impaired secretory pathway. In yeast, secretory vesicles deliver raw materials for the growth of the new bud. Any mutations in the pathway will render the cell dead. So there is a need to selectively induce the phenotype at restrictive temperatures. By using temperature sensitive mutants, Schekman identified 23 genes required for the secretory pathway.[2]


  1. ^ "Permissive temperature". Biology-Online Dictionary. 
  2. ^ Novick, P.; Field, C.; Schekman, R. (August 1980). "Identification of 23 complementation groups required for post-translational events in the yeast secretory pathway". Cell. 21 (1): 205–215. doi:10.1016/0092-8674(80)90128-2. ISSN 0092-8674. PMID 6996832.