Synthesis and metabolism of uracil-containing deoxyribonucleic acid in Escherichia coli

Significant amounts of uracil were found in the deoxyribonucleic acids (DNAs) of Escherichia coli mutants deficient in both uracil-DNA glycosylase (ung) and deoxyuridine 5'-triphosphate nucleotidohydrolase (dut) activities, whereas little uracil was found in the DNAs of wild-type cells and cells deficient in only one of these two activities. The amounts of uracil found in the DNAs of dut ung mutants were directly related to the growth temperature of the cultures, apparently because the deoxyuridine 5'-triphosphate nucleotidohydrolase synthesized by dut mutants was temperature sensitive. The dut mutant used failed to grow exponentially, became filamentous at temperatures above 25 degrees C, and exhibited a hyperrec phenotype; however, the ung mutation suppressed all of these effects. Although the dut ung mutants grew exponentially at all temperatures, their growth rates were always slower than the growth rate of the wild type. Since pool size measurements indicated that both deoxyuridine triphosphate and deoxythymidine triphosphate pools were markedly elevated in dut mutants, the reduced growth rate of dut ung cells apparently was due to the actual presence of uracil in the DNA, rather than to a deficiency of deoxyuridine triphosphate and deoxyribosylthymine triphosphate for DNA synthesis. The presence of uracil in E. coli donor DNA also markedly reduced the recombination frequency when the recipient cells were ung+, indicating that DNA repair commenced before the entering DNA could be replicated.     

tif-Stimulated deoxyribonucleic acid repair in Escherichia coli K-12

Bacterial survival is significantly increased after ultraviolet irradiation in tif sfi cells, provided that the thermosensitive tif mutation has been expressed at 41 degrees C before irradiation. This tif-mediated "reactivation of ultraviolet irradiated bacteria" needs de novo protein synthesis, as is the case for the tif-mediated reactivation of ultraviolet-irradiated phage lambda. However, in striking contrast to the phage reactivation process, this tif-mediated reactivation is no longer associated with mutagenesis. It also requires the presence of the uvrA+ excision function. These results strongly suggest the existence in Escherichia coli K-12 of a repair pathway acting on bacterial deoxyribonucleic acid which is inducible, error free, and uvr dependent.     

Trans-dominant mutation affecting restriction and modification in Escherichia coli K-12

Summary We have analysed the mechanism of action of a ts mutation in E. coli, which has an effect on the expression of the restriction and modification phenotype. The frequencies of recombinants obtained in transduction experiments support the idea that the temperature sensitive mutation is located outside the hsd operon in the gene denoted hsd. X. Complementation experiments demonstrated the trans-dominant nature of the temperature sensitive mutation. The possible role of the hsd.X product in the formation of EcoR.K and EcoM.K complexes and their interaction with the recognition site on the DNA is discussed.     

Nature of transforming deoxyribonucleic acid in calcium-treated Escherichia coli.

A study of the reactivation of ultraviolet-irradiated plasmid and phage deoxyribonucleic acid molecules after transformation into Escherichia coli strains indicated that, when double-stranded deoxyribonucleic acid was used as the donor species, it was taken up without conversion to the single-standed form.     

Medium-dependent variation of deoxyribonucleic acid segregation in Escherichia coli.

The degree to which deoxyribonucleic acid segregates nonrandomly has been investigated for Escherichia coli B/r growing in different media. The degree of nonrandom segregation observed is dependent on the medium, with segregation becoming less random as the growth rate decreases. This indicates that there must be some varying probabilistic component to the segregation process. A probabilistic modification of the Pierucci-Zuchowski model is proposed as well as a probabilistic model, in which it is proposed that deoxyribonucleic acid strands segregate, with a probability greater than 0.5, in the same direction (toward the same pole) as at the previous cell division.     

Penicillin selection of Escherichia coli deoxyribonucleic acid repair mutants.

A rapid method has been developed for isolation of ultraviolet-sensitive mutants of Escherichia coli, by inducing delay in the growth and/or division of repair-deficienct cells with low fluences of far-ultraviolet radiation, and killing with penicillin the repair-proficient cells, which continue to grow and divide. With this technique, we have achieved about a 3,000-fold enrichment for photoreactivation less (phr) cells and have isolated and characterized three phr mutants.