Temperature mutating effect

SAFETY PROFILE A human poison by an unspecified route. Poison by ingestion and intravenous routes. Moderately toxic by intraperitoneal route. Human systemic effects by ingestion hallucinations and distorted perceptions, sleepiness, constipation, cyanosis, respiratory stimulation, kidney damage, methemoglobinemia-carboxyhemoglobinemia, and decreased body temperature. Mutation data reported. When heated to decomposition it emits toxic fumes of NOx. Combustible when exposed to heat or flame. See also ANILINE. 

Temperature-sensitive mutations usually arise from a single mutation s effect on the stability of the protein. Temperature-sensitive mutations make the protein just unstable enough to unfold when the normal temperature is raised a few degrees. At normal temperatures (usually 37°C), the protein folds and is stable and active. However, at a slightly higher temperature (usually 40 to 50°C) the protein denatures (melts) and becomes inactive. The reason proteins unfold over such a narrow temperature range is that the folding process is very cooperative—each interaction depends on other interactions that depend on other interactions. 

For a number of temperature-sensitive mutations it is possible to find (or make) a seond mutation in the protein that will suppress the effects... 

The effects of various rhinovirus manipulations. The solid line depicts the native rhinovirus uncoating profile. Mutations and drugs can effect this profile to make the virus more or less stable to pH- or temperature-induced changes. 

Fig. 21. Proposed effects of random mutation and selection for activity on the stability of an enzyme evolving at a given temperature. Stability fluctuates within a range determined by the destabilizing influence of accumulating random mutations and by the minimal stability that is required to remain folded and functional.

The discoveries of Csp s and trigger factor may represent the tip of a large iceberg. In view of the pervasive effects of low temperature on the structures of all classes of macromolecules, it is reasonable to conjecture that many more types of proteins will be discovered whose roles are to offset the effects of cold shock on the cell. Some of these molecules may be expressed constitutively and may be part of the normal machinery of the cell. For example, certain ribosomal proteins are thought to function as RNA chaperones, and if present in sufficient amounts, these proteins may allow the cell to cope with the effects of cold shock on the structures of certain classes of RNAs. In yeast, a constitutively expressed ribosomal protein has helicase activity, and mutation in the gene encoding the protein confers on the cells a cold-sensitive phenotype (Schmid and Linder, 1992). Perhaps the apparent absence of cold-induced RNA chaperones in eukaryotic cells is... 

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