Determination of mutation rates in bacteriophage T4 by unneighborly base pairs: Genetic analysis |
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Authors: | Mark A Conkling Robert E Koch John W Drake |
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Institution: | 1. Department of Microbiology, University of Illinois, Urbana, Ill., U.S.A.;2. Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, N. C. 27709, U.S.A. |
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Abstract: | Earlier studies showed that the 2-aminopurine-induced mutation rate at a particular base pair can be influenced by the base adjacent to, or one additional base-pair removed from, the measured site (Koch, 1971). The present study extends to 0.3 map unit (about 30 base pairs) the distance at which a single base-pair substitution can exert such an effect. A particular base-pair substitution (defined as a ts mutation in the rIIA gene of bacteriophage T4) reduces the spontaneous, 2-aminopurine-induced and nitrous acid-induced reversions of an rIIA amber mutation approximately threefold. The ts mutation also reduces the 2-aminopurine-induced conversion of the corresponding ochre codon to amber (UAA → UAG) about twofold and to opal (UAA → UGA) about eightfold. The 2-aminopurine-induced reversion of the ochre codon to a glutamine codon (UAA → CAA), however, is not affected. Control experiments demonstrate that these observed reductions in mutation frequency do not result from unacceptable pathways of reversion in the presence of the ts allele. |
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Keywords: | Author to whom requests for reprints should be addressed at N I E H S Research Triangle Park N C 27709 U S A |
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