The effects of host-cell reactivation on assay of U.V.-irradiated Haemophilus influenzae transforming DNA

Genetic analysis of repair of ultraviolet damage by competent and noncompetent cells of Bacillus subtilis

The repair of ultraviolet (UV) damage in Bacillus subtilis W23T(-) has been studied by transformation with deoxyribonucleic acid (DNA) extracted from irradiated cells before and after repair. The extent of repair of genetic markers by donor cells after low or moderate doses of UV was found to be related only to the initial degree of inactivation. After a very high dose, further inactivation occurred, also in proportion to initial damage. In addition, the competent recipient cells were shown to repair approximately 75% of the damage in transforming DNA. The sensitivities of markers irradiated either in vivo or in vitro appeared to be related to map position, the more proximal markers showing a greater resistance to UV inactivation.

Ultraviolet irradiation of the vegetative cells of Dictyostelium discoideum

Experiments on the effect of ultraviolet (UV) light on the survival of vegetative Dictyostelium discoideum cells indicate that this is a relatively UV-resistant organism. Several factors suggest the presence of some type of repair process. Experiments to test for liquid-holding recovery and simple photoreactivation yielded negative results. Acriflavine and caffeine were utilized to possibly interfere with dark repair. Acriflavine produced no UV sensitization, but caffeine did cause a concentration-dependent decrease in survival of irradiated cells. When UV-irradiated cells were illuminated with photoreactivating light while suspended in caffeine, the survival increased above that for cells treated with caffeine alone, suggesting an overlap between lesions repaired by photorepair and dark repair. Growth experiments showed that UV light induced a dose-dependent division delay, followed by a period of retarded growth characterized by the presence of a constant fraction of nonviable cells in the irradiated population. The delayed exposure of cells to caffeine after irradiation showed that the magnitude of the caffeine sensitization diminished throughout the division-delay period. An action spectrum indicated probable nucleoprotein involvement in the induction of division delay. UV light retarded ribonucleic acid and protein synthesis and temporarily blocked deoxyribonucleic acid synthesis. However, synthesis of all three accelerated prior to the end of the division-delay period and then closely paralleled the increase in cell number.

Endonuclease from Micrococcus luteus which has activity toward ultraviolet-irradiated deoxyribonucleic acid: its action on transforming deoxyribonucleic acid

An endonuclease purified from Micrococcus luteus makes single-strand breaks in ultraviolet (UV)-irradiated, native deoxyribonucleic acid (DNA). The purified endonuclease is able to reactivate UV-inactivated transforming DNA of Haemophilus influenzae, especially when the DNA is assayed on a UV-sensitive mutant of H. influenzae. After extensive endonuclease action, there is a loss of transforming DNA when assayed on both UV-sensitive and -resistant cells. The endonuclease does not affect unirradiated DNA. The results indicate that the endonuclease function is involved in the repair of biological damage resulting from UV irradiation and that the UV-sensitive mutant is deficient in this step. We interpret the data as indicating that the various steps in the repair of DNA must be well coordinated if repair is to be effective.

Mutants of Diplococcus pneumoniae that lack deoxyribonucleases and other activities possibly pertinent to genetic transformation

Mutants of Diplococcus pneumoniae that lacked the two major deoxyribonucleases of the cell-one an endonuclease, the other an exonuclease preferentially active on native deoxyribonucleic acid (DNA)-were obtained. The development of a method for detecting mutant colonies, based on the binding of methyl green to DNA, facilitated isolation of the mutants. Neither enzyme was essential for growth of the cells, for repair of ultraviolet damage, or for any phase of DNA-mediated transformation. Residual deoxyribonuclease activity in the double mutant corresponded to an exonuclease, approximately one-fifth as active as the major exonuclease, that attacked native and denatured DNA equally well. This activity appeared to be associated with the DNA-polymerase enzyme. A mutant that apparently lacked a cell wall lytic enzyme was also fully transformable. A mutant strain that was four times more sensitive to ultraviolet light than the wild type also transformed normally. Recipient cells of this strain were deficient in the repair of ultraviolet-irradiated transforming DNA. Mutants were found which, unlike the wild type, integrated donor markers only with high efficiency, thereby indicating that a particular cellular component that is susceptible to loss by mutation, such as an enzyme, is responsible for low integration efficiency.

Recovery of colony-forming ability and genetic marker activity by UV-damaged Hemophilus Influenzae

The rate of recovery of UV-irradiated Hemophilus influenzae from acriflavine-sensitized loss of colony-forming ability was studied at various acriflavine concentrations, UV doses, and temperatures. This rate (as calculated from an equation based upon certain assumptions) was on the order of 0.07 per minute per cell at 37 degrees C. This did not vary greatly with UV dose or acriflavine concentration, but did with temperature, giving a DeltaHdouble dagger of about 16 kcal/mole. In another set of experiments, cells bearing two genetic markers (resistance to 2000 mug/ml streptomycin and to 2.5 mug/ml novobiocin) were irradiated and then incubated without acriflavine. DNA extracts made from samples taken after various periods of incubation time were assayed on antibiotic-sensitive cells using acriflavine to inhibit repair during and following transformation. It was found that both in vivo irradiated markers were reactivated in the donor to approximately the same extent (with a rate constant of 0.04 per minute). This result was in contrast to the results obtained when extracted DNA bearing the same markers was irradiated in vitro and used to transform cells. In this latter case the streptomycin marker was much more sensitive than the novobiocin marker. This difference is interpreted as being due to the mechanics of the transformation system.

Repair of deoxyribonucleic acid in Haemophilus influenzae. I. X-ray sensitivity of ultraviolet-sensitive mutants and their behavior as hosts to ultraviolet-irradiated bacteriophage and transforming deoxyribonucleic acid

Seven mutants of Haemophilus influenzae were isolated by the criterion of sensitivity to ultraviolet (UV) inactivation of colony formation. These mutants and the wild type were characterized with regard to X-ray inactivation of colony formation, UV induction of division inhibition, the ability of the eight strains to act as recipients to UV-irradiated H. influenzae phage and transforming deoxyribonucleic acid (DNA), and the influence of acriflavine on the survival of UV-irradiated transforming DNA with these strains as recipients. The photoreactivable sector of transforming DNA with yeast photoreactivating enzyme was measured for the most UV-sensitive mutant and was found to be greater than that of wild type. Judged by the above criteria, the order of the strains' sensitivities shows some, but by no means complete, correlation from one type of sensitivity characterization to another, indicating that a minimum of two variables is needed to explain the differences in the strains. Acriflavine increases the UV sensitivity of transforming DNA except in the most sensitive mutant. This effect is usually, but not always, more pronounced in the case of the more UV-resistant marker. The acriflavine effect is postulated to be the result of at least two factors: (i) interference with repair of transforming DNA in the host cell, and (ii) interference with the probability of recombination between transforming DNA and host DNA.