Repair of a double-stranded gap in plasmid DNA in radiosensitive mutants of Saccharomyces cerevisiae: effectiveness and precision

The repair of a double strand gap in plasmid DNA in radiosensitive mutants of Saccharomyces cerevisiae has been studied. The proportion of repair events resulting in the complete doublestrand gap recovery of the plasmid DNA has been found to be close to 100% in Rad+ cells. The mutation rad55 did not interfere in the doublestrand gap repair efficiency and accuracy. The mutant rad57 is capable of the effective doublestrand gap repair without restoration of the DNA sequence deleted by the gap. The mutation rad53 substantially inhibited the efficiency of the doublestrand gap repair but did not influence the accuracy of the repair. Plasmid DNA doublestranded gap repair is completely blocked by mutations rad50 and rad54.     

Phenotypic and Genetic Analysis of a Mutant of Heterorhabditis bacteriophora Strain HP88

Induction and characterization of a morphological mutant are described for Heterorhabditis bacteriophora strain HP88. A homozygous inbred line was used as the base population for mutagenesis and genetic analysis of mutations. Mutagenesis was induced by exposing young hermaphrodites to 0.05 M ethyl methanesulfonate. A dumpy mutant (designated Hdpy-l) was isolated from the F₂ generation of the mutagenized population. Morphological studies with light and scanning electron microscopy revealed that the head region of the adult stage was compressed. The head region of the infective juvenile was distorted and the mouth open. Backcross with the original population was successful only between mutant hermaphrodites and wild type males; 50-100 percent of the progeny of this cross maintained the dumpy phenotype, indicating that the ratio between self- and external fertilization of the eggs is > 1 and that the dumpy mutation is recessive.