Forward mutations

Forward mutations leading to a loss of function can be of two types mutations leading to loss of an enzymic function required for biosynthesis, resulting in a growth factor requirement, and mutations leading to resistance to various toxic chemicals and substrate analogues. 

cerevisiae, and Leupold established the same situation for Schiz-pombe. Since mutation of at least five gene loci can be detected starting with a red mutant, the optical yield of a mutation experiment is much better. Moderate doses of a good mutagen may yield white mutations at frequencies around 5%. Heslot 29) used this system for mutagenesis experiments in Schiz- pomhe, and in Sacch. cerevisiae this became quite popular, too. Marquardt et used seven mutagens to test, as was 

Snow 33) has described a method to enrich auxotrophic mutants in Saccharomyces and Megnet 34) a method for the same in Schizosac-charomyces using nystatin and 2-deoxyglucose, respectively. These methods have been useful in many hands in obtaining auxotrophic mutants, but. 

In conclusion, there are a few practicable systems for auxotrophic mutations available which do not involve replica plating or other after-treatment manipulations and require only plating and visual screening of plates. Since the majority of auxotrophic mutations are recessive, work is restricted to haploid cells. There are published reports on mutagenesis in diploid yeast which started out with diploids heterozygous for red adenine mutations. The mutation frequencies observed are usually impressive but most of the time are due to mitotic crossing-over or gene conversion (see Zimmermann et Nevertheless, such a diploid 

According to Siegal and Sisler, cycloheximide resistance is due to an alteration in ribosomal protein. A mutation in the respective structural gene(s) of the nonsense or frameshift type most certainly will lead to the formation of a completely nonfunctional protein which will be lethal. Therefore, only missense or very terminal nonsense or frameshift mutations can be expected to lead to the formation of a functional protein which causes resistance against cycloheximide. ICR-170 is considered to be a frameshift mutagen, and consequently it is not able to induce the required type of mutation. 

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TK or HPRT forward mutation assays in cultured mammalian ceils Drosophila sex-linked recessive lethal assay... 

McGregor DB, Brown A, Cattanach P, et al. 1988. Responses of the L5178Y tk+/tk- mouse lymphoma cell forward mutation assay III. 72 coded chemicals. Environ Mol Mutagen 12 85-154. 

Forward mutation refers to mutation of the natural ( wild-type ) organism to a more stringent organism. By contrast, reverse (backward) mutation is the return of a mutant strain to the wild-type form, i.e. it is a heritable change in a previously mutated gene that restores the original function of that gene. 

Salmonella typhimurium (reverse mutation) Escherichia coli (forward mutation, DNA modification) Saccharomyces cerevisia (reverse mutation) Bacillus subtilis (rec assay) Gene mutation or DNA modification Bruce and Heddle 1979 Dunkel et al. 1984 Fukunaga et al. 1982 Kharab and Singh 1985 Nestmann et al. 1979 Nishioka 1975 Rosenkranz and Poirier 1979 Simmon 1979b... 

McGregor, D.B., A.G.Brown, S.Howgate, D.McBride, C.Riach, and W.J.Caspary. 1991. Responses of the L5178Y mouse lymphoma cell forward mutation assay. V. 27 coded chemicals. Environ. Mol. Mutagen. 17 196-219. 

In a study using cultured L5178Y mouse lymphoma cells, Rogers and Back (1981) reported that both 1,1-dimethylhydrazine and 1,2-dimethylhydrazine induced forward mutations at the thymidine kinase level in the absence of an extraneous metabolic activation system. The investigators also noted that the two dimethylhydrazines appeared to have different modes of action under these conditions. 

The mouse lymphoma forward mutation test at the thymidine kinase locus (detects mutations to a nonfunctional thymidine kinase in a line of culture mouse lymphoma cells). 

Macgregor, J.T., D.H. Gould, A.D. Mitchell, and G.P. Sterling. 1979. Mutagenicity tests of diflubenzuron in the micronucleus test in mice, the L5178Y mouse forward mutation assay, and the Ames Salmonella reverse mutation test. Mutat. Res. 66 45-53. 

Forward Mutation Tests. Forward mutation is an endpoint that may arise from various events, including base substitutions, frameshifts, DNA deletions, and so on, as mentioned earlier. 

Mouse 1umphoma cells Forward mutation No data... 

Prokaryotic organisms Escherichia coll Sd-4 (forward mutation)... 

Mouse lymphoma cells (L5178YTK+/-) (forward mutation) Gene mutation No data + Kramers et al. 1985... 

Recessive lethal Forward mutation Forward mutation Forward mutation Forward mutation... 

Chinese hamster ovary cells liquid media Forward mutation + + Tan and Hsie 1981 Brimer et al. 1982... 

Mouse lymphoma L5178Y/liquid media Forward mutation + + Clive et al. 1979 NTP 1989... 

Human epithelial cells liquid media Forward mutation No data + Ferrer et al. 1983... 

Crebelli R, Bellincampi D, Conti G, et al. 1986. A comparative study on selected chemical carcinogens for chromosome malsegregation, mitotic crossing-over and forward mutation induction in Aspergillus nidulans. Mutat Res 172 139-149. 

Dichlorophenol with or without metabolic activation did not induce an increase in mutagenic response in the Chinese hamster ovary HGPRT forward mutation assay (Litton Bionetics 1986a). This compound was also inactive in the Balb/3T3 in vitro transformation assay (Litton Bionetics 1985). 

Litton Bionetics. 1986a. Mutagenicity evaluation of 2,5-dichlorophenol in the CHO HGPRT forward mutation assay. Report to Bayer AG Institut Fuer Toxicology, West Germany, by Litton Bionetics, The Netherlands. 

The genotoxicity of fuel oil no. 2, kerosene, and diesel fuel was also evaluated with the mouse lymphoma TK" " forward mutation assay (Conaway et al. 1984). The data reported was insufficient to permit a full evaluation of the results however, the authors considered diesel fuel and kerosene to be negative and fuel oil no. 2 to be positive. 

The test is used to detect forward and reverse gene mutation in Aspergillus nidulans, a eukaryotic fungus. These mutations are detected by changes in colonial morphology or nutritional requirements in treated populations. The methionine and 2-thioxanthine forward mutation systems can be used to detect mutations in Aspergillus nidulans. 

A variety of mammalian cell culture systems can be used to detect mutations induced by chemical substances. The L5178Y mouse l)nnphoma line, measuring mutation at the TK locus, is preferred. TK is an important enz)une involved in DNA synthesis. Cells are exposed to the test substance at various concentrations, in the presence and absence of a metabolic activation system, for a suitable period of time, and then subcultured to assess cytotoxicity and to allow phenotypic expression prior to mutant selection. Cells deficient in TK because of a forward mutation are resistant to the cytotoxic effects of pyrimidine analogues (antimetabolites), such as trifluorothymidine (TFT). This is because the antimetabolites cannot be incorporated into cellular nucleotides and kill the cell through inhibition of cellular metabolism. After treatment, cells are grown in a medium containing TFT mutant cells can proliferate in the presence of TFT, whereas normal cells containing TK are killed. This allows the detection of an increase in mutant... 

Forward mutation Unscheduled DNA synthesis Chromosomal aberrations Sister chromatid exchange... 

Eukaryotic organisms (i n vi trn) Mammalian cells L5178Y mouse lymphoma cells 1988c Forward mutation - - Hazleton Labs... 

L5178Ye mouse lymphoma cells 1988c Forward mutation - Hazleton Labs... 

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