Ultraviolet mutagenesis studies of [psi], a cytoplasmic determinant of Saccharomyces cerevisiae.

UV mutagenesis was used to probe the molecular nature of [psi], a nonmitochondrial cytoplasmic determinant of Saccharomyces cerevisiae involved in the control of nonsense suppression. The UV-induced mutation from [psi+] to [psi-] showed characteristics of forward nuclear gene mutation in terms of frequency, induction kinetics, occurrence of whole and sectored mutant clones and the effect of the stage in the growth cycle on mutation frequency. The involvement of pyrimidine dimers in the premutational lesion giving the [psi-] mutation was demonstrated by photoreactivation. UV-induced damage to the [psi] genetic determinant was shown to be repaired by nuclear-coded repair enzymes that are responsible for the repair of nuclear DNA damage. UV-induced damage to mitochondrial DNA appeared to be, at least partly, under the control of different repair processes. The evidence obtained suggests that the [psi] determinant is DNA.

[Elimination of extrachromosomal streptomycin resistance in staphylococci by experimental variations in geomagnetic field intensity]. / Eliminirovanie ékstrakhromosomnoi streptomitsinorezistentnosti u stafilokokkov pri éksperimental'nykh variatsiiakh napriazhennosti geomagnitnogo polia.

The article comprises the data on the elimination of streptomycin resistance in Staphylococcus aureus after its passage for a long time in a low permanent magenetic field (PMF) with H = 0.5 oe and in a space screened from the geomagnetic field in a permaloy chamber (H = 10(-2). Under these conditions the eliminating effect of the geomagnetic field intensity on the streptomycin resistance of Staphylococci became perceptible after 5--10 their passage under unusual conditions. At the next stages of investigation the eliminating effect of low PMF and of screening was enhanced. At the end of the experiment after 25--40 passages of Staphylococcus aureus throung MF of different intensity the elimination of streptomycin resistance was recorded in all the 11 cultures studied. The quantity of eliminates in populations of experimental substrains of Staphylococcus increased by 1.5--10 and more times as compared to the control.

[Increase in resistance to UV-light in E. coli bearing the Hly plasmid resistance]. / Povyshenie ustoichivosti k UF-svetu u E. coli, nesushchikh plazmidu Hly

Hly plasmide of wild type and its derepressive (by transmission) mutant communicated to the E. coli cells an increased resistance to the action of ultraviolet rays. Hly plasmide failed to compensate the defects associated with the excision and postreplicative DNA reparation or the reparative DNA synthesis. Hly plasmide increased the resistance to the ultraviolet light in the lon--mutant in which the ultraviolet irradiation disturbed the process of cell division. It is supposed that the resistance to the ultraviolet light connected with Hly plasmide was caused by the influence of the plasmide on some stages of cell division following the ultraviolet irradiation.

[Genetic nature of the bacteriocinogenicity factor of Staphylococcus epidermidis strain No. 259]. / Issledovanie geneticheskoi prirody faktora bakteriotsinogennosti shtamma Staphylococcus epidermidis No. 259.

Genetic nature of the bacteriogenicity factor of the Staphylococcus epidermidis No. 259 strain was studied by acting upon the strain with ultraviolet irradiation, acridine orange at a temperature of 37 and 44 degrees C, and cultivation of the strain at a temperature of 44 degrees C for 24 and 96 hours. The most effective elimination of the bacteriocinogenicity factor was reached with the action of acridine orange at 44 degrees C and the strain passage at 44 degrees C for 96 hours. A study of 212 subcultures which lost the bacteriocinogenicity factor under the effect of various factors demonstrated that they failed to differ by properties from the initial strain and retained the bacteriocin resistance of the initial strain. A conclusion was drawn that the bacteriocinogenicity factor was an extrachomosomic agent, and was not associated with any other strain properties.

Environment factors can influence mitochondrial inheritance in the fungus Cryptococcus neoformans.

Cryptococcus neoformans is a model basidiomycete yeast. Strains of this species belong to one of two mating types: mating type a (MATa) or mating type alpha (MATalpha). In typical crosses between MATa and MATalpha strains, the progeny inherit mitochondria from the MATa parent. However, the underlying mechanisms remain largely unknown. To help elucidate the molecular mechanisms, we examined the effects of four environmental factors on the patterns of mtDNA inheritance. These factors are temperature, UV irradiation, and the addition of either the methylation inhibitor 5-aza-2'-deoxycytidine (5-adc) or the ubiquitination inhibitor ammonium chloride. Except temperature, the other three factors have been shown to influence organelle inheritance during sexual mating in other eukaryotes. Our results indicate that while the application of 5-adc or ammonium chloride did not influence mtDNA inheritance in C. neoformans, both UV irradiation and high temperature treatments did. Progeny from a cross involving a high temperature-sensitive mutant with the calcineurin subunit A gene deleted showed biparental mtDNA inheritance in all examined temperatures, consistent with a role of calcineurin and temperature in mtDNA inheritance. Furthermore, the zygote progeny population from a cross performed at a high-temperature environment had a greater variability in their vegetative fitness than that from the same cross conducted at a low temperature. Our results indicate a potentially adaptive role of biparental mtDNA inheritance and mtDNA recombination in certain environments in C. neoformans.

Genetic fusion of incompatible plasmids in Pseudomonas.

The genes specifying enzymes responsible for the degradation of camphor and octane occur on transmissible plasmids in Pseudomonas putida strain PpG1 and P. oleovorans. Since the presence of the plasmids is vital for the oxidative metabolism of camphor or octane (by the cells) in the absence of other carbon sources, such naturally occurring, energy-generating plasmids have been designated as degradative plasmids. The two degradative plasmids, CAM and OCT, are incompatible with each other and cannot coexist in the same cell. By the use of UV irradiation and suitable selection techniques, it has been possible to fuse these two plasmids so they become part of the same replicon and coexist. Such a technique might be useful in introducing several degradative pathways in the same cell.