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    A GENETIC ANALYSIS OF NEW ASPECTS OF DNA REPAIR IN ESCHERICHIA COLI K-12

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    Author
    Pacelli Rassenti, Laura Zina
    Issue Date
    1981
    Keywords
    Escherichia coli.
    DNA repair.
    Bacterial genetics.
    Advisor
    Mount, David
    
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    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Abstract
    When the DNA of Escherichia coli is damaged a set of events termed "SOS functions" occur to aid cellular survival. The recA and lexA proteins are involved in the regulation of these functions. To determine the role of the lexA protein, amber mutations, designated spr-55(amber), were isolated in the lexA-3 gene. The lack of the lexA-3 gene product abolished sensitivity to ultraviolet light and resulted in the constitutive synthesis of recA protein. Introduction of amber suppressor mutations restored the original lexA-3 phenotype. It was concluded that spr mutations inactivate lexA protein resulting in the constitutive expression of the SOS functions. These data provide evidence that the lexA protein is the repressor for the recA gene. The repair of phage lambda (λ⁺) by ultraviolet light was determined in the strains carrying alleles of the spr, uvrA, and recA genes. The survival of the phage was more in the spr-51 uvrA⁺ strain as compared to wild type. These results were not dependent on the recA genotype. Introduction of the uvrA-6 mutation into the spr-51 uvrA⁺ recA⁺ strains resulted in the same relative decrease of phage survival. These results suggest that lexA protein is involved in the regulation of uvrA-dependent excision repair and that inactivation of lexA leads to the constitutive expression of excision repair. New mutant forms of lexaA protein were isolated. The lexA⁺, lexA-3, lexA-10, and lexA-27 proteins displayed identical mobilities in the Weber and Osborn gel system. The lexA-10 and lexA-27 genes showed different phenotypes and encoded proteins of different mobilities in the Laemmli gel system. It was concluded that the differences in mobilities observed in the Laemmli gel system are due to alterations in charge or amino acid, not in size; furthermore; the molecular weight of lexA⁺ protein was determined to be 24 kilodaltons.
    Type
    text
    Dissertation-Reproduction (electronic)
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Graduate College
    Genetics
    Degree Grantor
    University of Arizona
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