Low glutathione pools in the original pso3 mutant of Saccharomyces cerevisiae are responsible for its pleiotropic sensitivity phenotype.

The original pso3-1 mutant isolate of the yeast Saccharomyces cerevisiae exhibits a pleiotropic mutagen-sensitivity phenotype that includes sensitivity to UVA-activated 3-carbethoxypsoralen, to UVC-light, to mono- and bi-functional nitrogen mustard, to paraquat, and to cadmium; on the other hand, it shows hyper-resistance (HYR) to nitrosoguanidine when compared to established wild-type strains. Also, the original pso3-1 mutant exhibits a low UVC-induced mutability and mitotic gene conversion and a high rate of spontaneous and UVC-induced petite mutations. Since the HYR to the nitrosoguanidine (MNNG) phenotype resembles that of low glutathione-containing yeast cells, the original pso3-1 mutant was crossed to a gsh1 knock-out mutant that lacks the enzyme for the first step in glutathione biosynthesis and the resulting diploid was tested for complementation. While there was none for HYR to nitrosoguanidine, and other low glutathione-related phenotypes, some other phenotypic characteristics of pso3-1, e.g. UVC sensitivity and UVC-induced mutability were restored to a wild-type level. Tetrad analysis of a diploid derived from a cross of the original haploid pso3-1 isolate with a repair-proficient, normal glutathione-containing, PSO3 GSH1 wild-type led to the separation of a leaky gsh1 mutation phenotype from that of the repair-deficient pso3-1 phenotype. Linkage studies by tetrad and random spore analyses indicated no linkage of the two genes. This shows that the low glutathione content in the original pso3-1 isolate is due to a second, additional, mutation in the GSH1 locus and is unrelated to the pso3-1 mutation. Thus, the original pso3-1 isolate is a pso3-1 gsh1 double mutant with most of the particular characteristics of the pleiotropic sensitivity phenotype contributed by either the pso3-1 or the gsh1-leaky mutant allele. The expression of a few phenotypic characteristics of pso3, however, were most pronounced in pso3-1 mutants with a low glutathione pool.

Beagle model used in a tissue tolerance study of the response of normal and surgically manipulated liver to single high-dose intraoperative radiotherapy.

To investigate the feasibility of delivering a single large dose of intraoperative electron beam radiotherapy (IORT) to the liver of clinically normal and partially hepatectomized beagles, an experimental study was designed. The purpose of the study was to obtain dose guidelines for the delivery of IORT to the liver of human patients with colorectal cancer metastases to the liver. After partial resection of the liver, IORT in doses up to 30 Gy was applied to the resection plane as well as to a nonsurgically manipulated part of the liver of 25 beagles. The temporal sequence of histologic changes of these irradiated parts of the liver tissue was investigated. There were no postoperative complications and no morbidity or mortality associated with a minimal follow-up of 3 years. Necropsy performed 3 months after IORT revealed only mild histopathologic changes. One year after IORT, more distinct histopathologic changes consisting of capsular thickening, diffuse parenchymal fibrosis, and subcapsular hepatocellular atrophy were found. Three years after IORT, the parenchymal architecture seemed to be restored, although loss of liver tissue was definitive at the irradiation site; liver function remained intact. These results indicate that IORT to part of the liver in the canine model can be safely applied and that, although doses up to 30 Gy can result in severe local tissue damage, wound healing and liver function are not disturbed.

Genetic characterization of hyperresistance to formaldehyde and 4-nitroquinoline-N-oxide in the yeast Saccharomyces cerevisiae.

The hyperresistance to 4-nitroquinoline-N-oxide (4-NQO) and formaldehyde (FA) of yeast strains transformed with the multi-copy plasmids pAR172 and pAR184, respectively, is due to the two genes, SNQ and SFA, which are present on these plasmids. Restriction analysis revealed the maximal size of SFA as 2.7 kb and of SNQ as 2.2 kb, including transcription control elements. The presence of the smallest 2.7 kb subclone carrying SFA increased hyperresistance to formaldehyde fivefold over that of the original pAR184 isolate. No such increase in hyperresistance to 4-NQO was seen with the smaller subclones of the pAR172 isolate. Disruption of the SFA gene led to a threefold increase in sensitivity to FA as compared with the wild type. Expression of gene SNQ introduced on a multi-copy vector into haploid yeast mutants rad2, rad3, and snm1 did not complement these mutations that block excision repair.