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The excision of thymine dimers from DNA, filament formation and sensitivity to ultraviolet light in Escherichia coli K-12

1964; Elsevier BV; Volume: 1; Issue: 3 Linguagem: Inglês

10.1016/0027-5107(64)90002-8

1873-135X

Paul Howard-Flanders, Eva Simson, Lee Theriot,

Bacterial Genetics and Biotechnology

Strains of Escherichia coli K-12 have been described previously that lack the ability to excise thymine dimers from DNA after UV irradiation, and are abnormally sensitive to UV light as regards the survival of colony forming ability. These strains carry mutations at the uvrA or uvrB loci which are linked to the loci for methionine requirement and for the λ prophage. Strains with a mutation at the lon locus, which is linked to the marker for T6 resistance, tend to grow in long forms, to form a mucoid capsule and to be abnormally radiosensitive to both UV light and to X-rays. This paper describes the properties of the double mutants uvr lon which are many times more sensitive to UV light than either of the single mutants. In genetic crosses with a wild type Hfr and a uvr lon female strain, the radiation resistance of recombinants was found to increase in two steps as the wild-type alleles of the lon and uvr loci entered the zygote. The survival of UV-irradiated Tr phage is affected by uvr, but not lon in the host bacterium used for plating. The results confirm that the uvr and lon genes affect sensitivity to radiation through independent mechanisms.