Studies on radiation-sensitive mutants of E. coli. I. Mutants defective in the repair synthesis

Conditional lethality of deletions which include uvrB in strains of Escherichia coli lacking deoxyribonucleic acid polymerase I

Deletions of the uvrB gene were not obtained in polA1 strains of Escherichia coli either by selecting for spontaneous deletions or by transduction from strains carrying such deletions. A strain forming a temperature-sensitive deoxyribonucleic acid polymerase I and carrying a deletion of the uvrB gene is inviable at the nonpermissive temperature.

Deletion and complementation analysis of biotin gene cluster of Escherichia coli

Genetic deletions that terminate within the cluster of genes needed for biotin biosynthesis in Escherichia coli have been isolated and mapped by transduction with phages lambda and P1. These deletions order the point mutations in each of the five genes. Mutations causing biotin dependence were incorporated into lambdapbio transducing phages. New bio(-) mutations were induced by exposure of lambdapbio particles to ultraviolet light. Tests of complementation between such bio(-)pbio particles and bio(-) mutant cells divide the bio(-) mutations into five cistrons: bioA, bioB, bioF, bioC, and bioD. Certain bioA and bioF mutations exhibit intragenic complementation, suggesting that these genes determine enzymes composed of identical subunits.

Dominant mutations (lex) in Escherichia coli K-12 which affect radiation sensitivity and frequency of ultraviolet lght-induced mutations

Three mutations, denoted lex-1, -2 and -3, which increase the sensitivity of Escherichia coli K-12 to ultraviolet light (UV) and ionizing radiation, have been found by three-factor transduction crosses to be closely linked to uvrA on the E. coli K-12 linkage map. Strains bearing these mutations do not appear to be defective in genetic recombination although in some conjugational crosses they may fail to produce a normal yield of genetic recombinants depending upon the time of mating and the marker selected. The mutagenic activity of UV is decreased in the mutant strains. After irradiation with UV, cultures of the strains degrade their deoxyribonucleic acid at a high rate, similar to recA(-) mutant strains. Stable lex(+)/lec(-) heterozygotes are found to have the mutant radiation-sensitive phenotype of haploid lex(-) strains.

Deoxyribonucleic acid repair in bacteriophage T4: observations on the roles of the x and v genes and of host factors

Studies were carried out to determine the effect of mutation in the host pol I gene on survival of ultraviolet (UV)-irradiated bacteriophage T4. Whereas a slightly reduced survival was observed in Escherichia coli strain P-3478 (pol A(1)) compared to strain W-3110 (pol A(+)), no such difference was observed in two strains isogenic except for the pol A gene. It was also shown that, whereas bacteriophage T4x is sensitive to UV irradiation, X irradiation, and treatment with methyl-methanesulfonate (MMS), phage T4v(1) is sensitive only to UV irradiation. The survival of damaged phage T4x is neither affected by the presence of the rec A, rec B, or pol A mutations in the host, nor is there evidence that phage T4 effects repair of rec A or pol A mutants previously treated with either UV or MMS.

Temperature-sensitive recovery of a mutant of Escherichia coli K-12 irradiated with ultraviolet light

URT-43 is a mutant of Escherichia coli K-12 which gives a much larger number of survivors when ultraviolet (UV)-irradiated bacteria are incubated on agar medium at 30 C than when they are incubated on the medium at 41 C, although in both cases the number of survivors is fewer than that given by its wild-type ancestor. The UV sensitivity of this mutant was found to be markedly influenced by the presence of a high concentration of NaCl or sucrose in the plating medium. Thus, when irradiated bacteria were plated on agar medium containing 2% NaCl or 0.5 m sucrose at 30 C, they exhibited a resistance similar to that of their wild-type ancestor. At 30 C, there was also an extensive recovery in liquid M9 medium supplemented with all of the nutrients required for growth and NaCl or sucrose. At 41 C, however, the recovery was greatly inhibited. Direct chemical analysis of thymine dimers has revealed that no significant amount of the dimer was released from deoxyribonucleic acid during the period of extensive recovery. It was concluded, therefore, that the temperature-sensitive recovery of URT-43 does not accompany excision of the bulk of pyrimidine dimers. To learn the gene function involved in the recovery, double mutants carrying an additional mutation either in a uvr or a rec gene have been investigated for their UV sensitivities and recovery in liquid medium. It was found that recA(-) and recB(-) derivatives retain the ability of undergoing an efficient recovery at a low temperature, whereas uvrB(-) and uvrC(-) derivatives have completely lost this ability. For these reasons, it was concluded that the mechanism responsible for the recovery of URT-43 involves the function controlled by the uvr genes. The results of photoreactivation suggested that most of the entities dealt with during recovery were pyrimidine dimers.

Ultraviolet- and X-ray-induced responses of a deoxyribonucleic acid polymerase-deficient mutant of Escherichia coli

Escherichia coli K-12, polAl(-) is a mutant strain whose extracts are deficient in Kornberg deoxyribonucleic acid (DNA) polymerase activity. We have compared the mutant and parental strains on the basis of a number of responses to ultraviolet (UV) and X-irradiation. For both types of radiation, the mutant is more sensitive by approximately the same factor as measured by reduction in colony formation, depression of DNA synthesis, and enhancement of DNA degradation. The rate of repair of X-ray-induced single-strand breaks in the mutant is also slower, as is the repair of breaks after excision repair of UV damage. On the other hand, the mutant has a significant capability to reactivate UV-irradiated lambda phage, although it is almost totally deficient in the ability to carry out UV reactivation. The data indicate that the polAl mutation leaves the cells with some ability to perform excision and strand-rejoining repair but that an exonuclease, whose identity remains obscure, is the agent responsible for the extensive breakdown of the DNA in polAl(-) cells after irradiation.

Mutation and recombination of bacteriophage lambda: effect of ultraviolet radiation

Defects in the bacterial recB or recC or phage red or int gene did not impair ultraviolet light-induced clear mutations of lambda phage. Clear mutants of cI and cII genes were not enriched among RecA-promoted UV-induced recombinants between the N and O genes which closely encompass the c genes. No correlation was observed between UV-induced mutation and genetic recombination.

Genetic and molecular characteristics of X-ray-sensitive mutants of Escherichia coli defective in repair synthesis

Alleles responsible for X-ray-sensitive characteristics of three mutants of Escherichia coli B, which were also sensitive to ultraviolet (UV) irradiation, were mapped near metE locus, and named res-1, res-2, and res-3. All the res(-) mutants showed no host cell reactivability (Hcr(-)) for transducing deoxyribonucleic acid (DNA) of P1 phage irradiated by UV but they were Hcr(+) for infective DNA of P1 phage. Furthermore, they showed no detectable activity of DNA polymerase. Characteristics of allele res-1 were studied in detail. The mutant res-1 uvr(+) showed an extensive degradation of DNA after UV irradiation. Double mutants carrying res-1 uvrA(-), res-1 uvrB(-), and res-1 uvrC(-) showed no marked increase in UV sensitivity beyond that of the uvr(-) single mutants and only negligible UV-induced DNA degradation. The uvr(-) mutations showed no such suppressive effect on DNA degradation induced by X rays in these double mutants. It is concluded that res(-) mutants are defective in the second step (repair synthesis) of the excision repair process and that DNA polymerase is partly responsible for the assumed resynthesis step.

Recombination-deficient mutants of colicinogenic Salmonella typhimurium detected by their failure to produce colicin

Survivors of nitrosoguanidine-treated cultures of a colicinogenic strain of Salmonella typhimurium were tested for spontaneous production of colicin E1. Of about 1,000 colonies tested, 13 produced no (or very narrow) colicin zones. Four of these isolates proved to be more sensitive to ultraviolet (UV) light, X rays, and methyl methane sulfonate than the parent strain and did not show enhanced production of colicin when treated with mitomycin C (which acts as an inducer on wild-type cells). Further studies showed that these isolates were of two classes. Three mutants were extremely sensitive to UV, failed to show spontaneous release of two temperate phages, and were infertile as recipients in transduction or in an Hfr cross although they accepted an F' factor normally. These independently isolated mutants were inferred to be recombination-deficient; one of them had the additional property of increased spontaneous mutability at two loci. The other colicin-nonreleasing isolate was only moderately sensitive to UV, showed enhanced spontaneous release of two temperate phages, and was of approximately normal fertility as a recipient in transduction or conjugation.

Genetic location in Escherichia coli K-12 of the ultraviolet-sensitive mutation uvrD3

A host cell reactivation-negative mutation, uvrD3, in Escherichia coli K-12 is located between ilv and metE.

Escherichia coli ras locus: its involvement in radiation repair

There are several classes of Escherichia coli mutants defective in radiation repair. These include strains defective in pyrimidine dimer excision, in photoreactivation, in recombination, in repair of X-ray damage, and ultraviolet (UV)-conditional mutants which do not divide after UV. Another mutant (ras(-)) has been isolated. The ras(-) has increased UV sensitivity, but only slightly increased X-ray sensitivity (1.5-fold increase). Ability to effect genetic recombination, to reactivate irradiated bacteriophage T1, and to be photoreactivated is normal. UV-induced mutation frequency is greatly increased in the mutant. The ras(-) apparently lacks the ability to repair some UV damage in the bacterial cell but can repair UV damage to bacteriophage DNA. The ras locus is located between lac and purE on the chromosome map.