Studies on Escherichia coli sex factors. II. Some physical properties of F'Lac and F DNA

Vegetative Replication and Transfer Replication of Deoxyribonucleic Acid in Temperature-Sensitive Mutants of Escherichia coli K-12

Crosses were carried out at 34 C and 42 C between eight pairs of isogenic strains of Escherichia coli K-12. The donor and recipient of each pair carried the same mutation for temperature-sensitive deoxyribonucleic acid (DNA) synthesis; they differed only in the presence of F-lac in the donor and a spectinomycin-resistance marker in the recipient. A different temperature-sensitive mutation was present in each of the eight pairs, the eight temperature-sensitive mutations being located in at least two different genes. In all eight pairs, the transfer of F-lac occurred at high and equal rates at 34 C and 42 C, although vegetative DNA replication at 42 C was approximately 10(-4) of that at 34 C. The transfer of F-lac at 42 C was accompanied in seven of the eight crosses by an equivalent amount of DNA synthesis in excess of that observed in the unmated controls. The DNA synthesized during transfer at 42 C was characterized by equilibrium centrifugation in cesium chloride and by its sedimentation velocity in sucrose gradients. It was found to have a density and a molecular weight characteristic of F-lac DNA. A small proportion of the material labeled during transfer was recovered in the form of covalently closed DNA. It is concluded that vegetative replication of the chromosome and transfer replication of F are separate processes, the former requiring at least two gene products which are nonessential for the latter.

Isolation of covalently closed circular deoxyribonucleic acid from Streptomyces coelicolor A3(2)

Covalently closed circular deoxyribonucleic acid (DNA) was isolated from two strains of Streptomyces coelicolor A3(2), representing two of the known fertility types. In each of the two strains circular DNA of about 20 times 10-6 daltons could be detected, amounting to about 1.5% of the total cellular DNA. The possible function of this DNA is discussed.

Influence of thymine starvation on the integrity of episomal and chromosomal deoxyribonucleic acids in Escherichia coli CR34 (lambda ind-)

The effect of thymine deprivation on the integrity of phage lambda, sex factor, and chromosomal deoxyribonucleic acid (DNA) in Escherichia coli CR34 (lambda ind(-)) was examined by sedimenting cell lysates through alkaline sucrose gradients. Both sex factor and chromosomal DNAs showed evidence of being degraded during the starvation period. In contrast, no loss of closed circular lambda DNA was observed.

Molecular structure of bacterial plasmids

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Properties of F' factor deoxyribonucleic acid transferred from ultraviolet-irradiated donors: photoreactivation in the recipient and the influence of recA, recB, recC, and uvr genes

Ultraviolet (UV)-irradiated Escherichia coli K-12 F lac(+) donors transfer damaged F' factors when mated with female cells. Exposure of the zygotes to white light after mating can cause the photoreactivation of the damaged transferred F' factors. In so far as the photoreactivation is specific for pyrimidine dimers, these experiments indicate the presence of UV-induced dimers in the transferred F' factor deoxyribonucleic acid (DNA). These damaged F' factors are remarkably stable in recA recipients, having a half-life for susceptibility to photoreactivation of 1.5 to 2 hr. This is judged by the formation of Lac(+) colonies, all of which are male secondary donors. In crosses with wild type and uvrA, recB, or recC mutant recipients, however, the Lac(+) colonies are predominantly recombinants and photoreactivation is not detected. The extent of DNA synthesis resulting from transfer of F' episomes from irradiated donors suggests that a complementary strand is formed on the damaged template. Photoreactivation behavior and sedimentation properties are used to deduce properties of such damaged episomes. We conclude that the complementary strand is discontinuous directly opposite dimers in the transferred strand. This structure may be an intermediate in the recombinational event sequence in Rec(+) recipients.

Nature of lactose-fermenting Salmonella strains obtained from clinical sources

Six of seven lactose-fermenting (lac(+)) Salmonella strains obtained from clinical sources were found to be capable of transferring the lac(+) property by conjugation to Salmonella typhosa WR4204. All of the six S. typhosa strains which received the lac(+) property transferred it in turn to S. typhimurium WR5000 at the high frequencies typical of extrachromosomal F-merogenotes. These six lac elements were also transmissible from S. typhosa WR4204 to Proteus mirabilis and to some strains of Escherichia coli K-12; moreover, they were capable of promoting low frequency transfer of chromosomal genes from S. typhimurium WR5000 to S. typhosa WR4204. One of these lac elements was shown also to be capable of promoting low frequency chromosome transfer in E. coli K-12. E. coli K-12 strains harboring these lac elements exhibited sensitivity to the male specific phage R-17. Sensitivity to R-17 was not detected in Salmonella strains containing the elements. Examination of the lac elements in P. mirabilis by cesium chloride density gradient centrifugation showed that each element had a guanine plus cytosine content of 50%. The sizes of the elements varied from 0.8 to 3% of the total Proteus deoxyribonucleic acid. The amount of beta-galactosidase produced by induced and uninduced cultures of S. typhimurium WR5000 and S. typhosa WR4204 containing the lac elements was lower than that produced by these strains with the F-lac episome. The heat sensitivity of beta-galactosidase produced by the lac elements in their original Salmonella hosts indicated that the enzyme made by these strains differs from E. coli beta-galactosidase.

Extrachromosomal inheritance in bacteria

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