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|Title:||Determination of Mutation Rates in Bacteriophage T4 by Unneighborly Base Pairs and a Genetic Analysis of the Error-Prone Repair System of Bacteriophage T4|
|Author(s):||Conkling, Mark Alan|
|Department / Program:||Microbiology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Earlier studies showed that the 2-aminopurine-induced mutation frequency of a particular base pair can be influenced by the base pair adjacent or penultimate to the measure site. This study extends to 0.3 map units (about 20-80 base pairs) the distance at which a single base-pair substitution can exert such an effect. The presence of a base-pair substitution (defined as a ts mutation in the rIIA gene) reduces the spontaneous and 2-aminopurine-induced reversion of an rIIA amber mutation approximately three-fold. This ts mutation also reduces the 2-aminopurine-induced conversion is reduced about eight-fold, while the reversion of the ochre codon to glutamine (UAA (--->) CAA) is not affected. Selection controls demonstrate that the decrease is not due to selection against the ts marker. Control experiments measuring the efficiencies of plating of various homologous nonsense mutations on the appropriate amino-acid-inserting suppressor strains demonstrate that the observed reduction is not due to the nature of the protein produced by the amino acid at the nonsense site. These results demonstrate that the intrinsic mutability of a given site can be influenced by neighboring base pairs across "long" physical distances.
"Error-prone repair" in bacteriophage T4 is mediated by at least three genes, uvsX, uvsY and uvsW. Mutants in these genes typically exhibit decreased UV-induced mutagenesis and increased sensitivity to UV-induced inactivation. Mutant alleles of uvsX and uvsY (but not uvsW) are shown to suppress mutants of gene 49. (Gene 49 is an essential gene whose product is involved in DNA packaging and head maturation.) Using suppression of gene 49 mutants as a selective force, amber and temperature-sensitive alleles of uvsX and uvsY were isolated and subsequently characterized for sensitivity to UV-induced inactivation and mutagenesis. The data indicate that three phenotypes exhibited by mutants of these genes (suppression of gene 49 mutants, increased sensitivity to UV-induced inactivation, and reduction of UV-induced mutation) may be uncoupled.
The temperature-sensitive alleles are used to study the time course of uvsX('+)/uvsY('+) mediated repair which is shown to occur in two phases, an almost immediate "early" phase and a late phase beginning about 20 minutes post infection.
The effects of temperature upon repair of UV-induced lesions was examined and a new property of repair was discovered. The rate of UV-induced inactivation of wild-type T4 increases with decreasing temperature. The effect is not seen in mutant alleles of uvsX or uvsY.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.
|Date Available in IDEALS:||2014-12-14|