Sensitizing Mutations

Mutation. For industrial appHcations, mutations are induced by x-rays, uv irradiation or chemicals (iiitrosoguanidine, EMS, MMS, etc). Mutant selections based on amino acid or nucleotide base analogue resistance or treatment with Nystatin or 2-deoxyglucose to select auxotrophs or temperature-sensitive mutations are easily carried out. Examples of useful mutants are strains of Candida membranefaciens, which produce L-threonine Hansenu/a anomala, which produces tryptophan or strains of Candida lipolytica that produce citric acid. An auxotrophic mutant of S. cerevisiae that requires leucine for growth has been produced for use in wine fermentations (see also Wine). This yeast produces only minimal quantities of isoamyl alcohol, a fusel oil fraction derived from leucine by the Ehrlich reaction (10,11). A mutant strain of bakers yeast with cold-sensitive metaboHsm shows increased stabiUty and has been marketed in Japan for use in doughs stored in the refrigerator (12). 

Temperature-sensitive mutations are those which allow a virus to replicate at one temperature and not at another, due to a mutational alteration in a virus protein that renders the protein unstable at moderately high temperatures. For instance, temperature-sensitive mutants are known in which the phage will not be replicated in the host at 43 °C but will at 25 °C, although the host functions at both temperatures. Such mutations are called conditionally lethal, since the virus is unable to reproduce at the higher temperature, but replicates at the lower temperature. 

DNA polymerase III has all the enzymatic activities of DNA polymerase I. A subunit of the enzyme is the product of the dna E gene. Temperature-sensitive mutations of this gene testify to the importance... 

Evidence for the first oncogene was found when certain mutants of RSV failed to transform cells at high temperature but did transform cells at low temperature. The mutant virus replicated well at both temperatures. This means that the virus contained a tem-perature-sensitive mutation in a gene that coded for a sarcoma-producing protein, that is, for v-src. 

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... 

Zuk D, Belk JP, Jacobson A (1999) Temperature-sensitive mutations in the Sacchammyces cerevisiae MRT4, GRC5, SLA2 and THS1 genes result in defects in mRNA turnover. Genetics 153 35-47... 

Exon Mutation Frequency In NSCLC Effect on TKL Exon Sensitivity Mutation... 

Cazzaniga G, Corradi B, Piazza R et al. Highly sensitive mutations detection in BCR-ABL positive leukemia prior and during imatinib treatment (Abstract 1985). Blood2004 104 548a. 

Temperature-sensitive mutations, in particular, have been very valuable in helping to define many of the proteins involved in replication. Several of these proteins have already been discussed. Temperature-sensitive mutations take effect at a certain temperature, e.g., 42-47°C, and not at another, e.g., 30°C or less. Mutations that affect replication are called dna mutations. Many that have been identified in E. coli code for various proteins associated with DNA chain growth at the replication fork. For example, the gene dnaG codes for primase (the DnaG protein) which has already been discussed. Some, however, code for proteins involved also or exclusively with the initiation of a cycle of replication at oriC. Examples of these are dnaA, B and C. 

Temperature-Sensitive Mutation. It is a special case of conditional mutation in which the restrictive condition is elevated or lowered temperature. Temperature-sensitive mutants are commonly used to analyze the function of essential genes, because inactivating mutations such as deletion mutations are not possible for these genes. 

Prokaryotic proteins related to IMPase have been characterized and a group of these are found on branch lb. The E. coli SuhB gene was isolated as a suppressor of many diverse temperature-sensitive mutations (Chang et al., 1991 Matsuhisa et al., 1995). Surprisingly, suppression of these unrelated phenotypes does not require active SuhB protein (Chen and Roberts, 2000). These authors characterized the SuhB protein and found that it too catalyzes the hydrolysis of inositol 1-phosphate with similar kinetics to the animal IMPases. However, EcSuhB can exist as a monomer unlike the dimers of other IMPases,... 

SAFETY PROFILE A human poison by inhalation. Experimental poison by inhalation, intraperitoneal, subcutaneous, and intravenous routes. Moderately toxic by ingestion and skin contact. Experimental reproductive effects. Corrosive. A severe skin and eye irritant. An allergen and sensitizer. Mutation data reported. Flammable liquid when exposed to heat, flame, or oxidizers. Can react violently with acetic acid, acetic anhydride, acrolein, acrylic acid, acrylonitrile, aUyl chloride, CS2, chlorosulfonic acid, epichlorohydrin, ethylene chlorohydrin, HCl, mesityl oxide, HNO3, oleum, AgC104, H2SO4, p-propiolactone, or vinyl acetate. To fight fire, use CO2, dry chemical, alcohol foam. When heated to decomposition it emits toxic fumes of NOx and NH3. See also AMINES. 

ENU) primarily function increase or decrease in toxicant sensitivity mutated gene... 

McClatchey AI, Van den Bergh P, Pericak-Vance MA et al 1992 Temperature-sensitive mutations in the III-IV cytoplasmic loop region of the skeletal muscle sodium channel gene in paramyotonia congenita. Cell 68 769—774... 

Adachi, Y., Yanagida, M. (1989). Higher order chromosome structure is affected by cold-sensitive mutations in a Schizosaccharomyces pombe gene crml, which encodes a 115-kD protein preferentially localized in the nucleus and its periphery. 

In haploid yeast cells, essential genes can be studied through the use of conditional mutations. Among the most common conditional mutations are temperature-sensitive mutations, which can be Isolated in bacteria and lower eukaryotes but not in warm-blooded eukaryotes. For Instance, a mutant protein may be fully functional at one temperature (e.g., 23 °C) but completely inactive at another temperature (e.g., 36 °C), whereas the normal protein would be fully functional at both temperatures. A temperature at which the... 

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