Mechanisms of DNA Repair as Revealed by Artificial Introduction of Enzymes into Viable Cells
Procedures for artificial introduction of active protein molecules into living cell systems have been developed and used to analyze cellular mechanisms for DNA repair. Plasmolyzed cells of Escherichia coli strains carrying a mutation in one of uvrA, uvrB and uvrC genes acquired ultraviolet (UV) resistance when the cells were exposed to high concentrations of T4 endonuclease V. With increasing concentrations of the enzyme, survival of the plasmolyzed cells after UV irradiation increased while colony-forming ability of unirradiated plasmolyzed cells was not significantly affected. The effect of T4 endonuclease V was specific for uvr mutants; wild type strains as well as strains having a mutation in recA or polA gene were not reactivated. On the other hand, E. coli DNA polymerase I was effective for enhancing survival of plasmolyzed cells of polA mutant, pre-exposed to UV. Thus, E. coli DNA polymerase I (molecular weight, 109,000 daltons) can be taken up into permeable cells and function in vivo to replace defective functions of the particular mutants.
KeywordsExcision Repair Xeroderma Pigmentosum Complementation Group Sendai Virus Artificial Introduction
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