Mapping of gene controlling thiamine transport in Saccharomyces cerevisiae.

A recessive mutation leading to complete loss of thiamine uptake in Saccharomyces cerevisiae was mapped on the left arm of chromosome VII, approximately 56 cM centromere-distal to trp5. As the analysed locus is relatively distant from its centromere and from the markers used, its attachment to chromosome VII was confirmed by chromosome loss methods.

Dipodascus magnusii (Saccharomycetes) contains multiple glucose-6-phosphate dehydrogenases with different NAD+/NADP+ dependencies.

A cell-free extract of a morphologically unstable strain of Dipodascus magnusii contained six proteins with activity of glucose-6-phosphate dehydrogenase (G6PDH). Two of these proteins displayed only NADP(+)-dependent activity, two could utilize both NAD+ and NADP+, but had higher activity with NAD+, and two possessed only NAD(+)-dependent activity. When the cultivation was carried out in the presence of monoiodoacetic acid, only two proteins with G6PDH activity were produced, one of them NAD(+)-dependent and the other NADP(+)-dependent. In all cases, NAD(+)-dependent activity was less stable in the presence of proteinases than was the NADP(+)-dependent activity.

Dominant resistance to oxythiamin in Saccharomyces cerevisiae and its mapping.

A dominant mutation, responsible for the resistance to oxythiamin in Saccharomyces cerevisiae was mapped on the right arm of chromosome IV, 4.6 cM centromere-distally to trp1. The corresponding gene is not involved in the control of intracellular content of total thiamin during growth on a minimal medium without thiamin.

The irreversibility of thiamin transport in Saccharomyces cerevisiae.

Neither exit nor counterflow efflux of thiamin, taken up previously by an active transport, were found in Saccharomyces cerevisiae, in either the wild type or a mutant with a lower rate of thiamin phosphorylation. Complete inhibition of thiamin phosphorylation by oxythiamin did not lead to any release of thiamin taken up by the cell.

Mutagenicity of glycerol chlorohydrines and of their esters with higher fatty acids present in protein hydrolysates.

3-chloro-1,2-propanediol and 1,3-dichloro-2-propanol caused base substitutions in Salmonella typhimurium TA1535 both with and without metabolic activation. Metabolic activation seemed to act mainly by decreasing the toxicity of these compounds. A difference in the growth of the wild-type and repair-deficient strains of Escherichia coli was observed only for 1,3-dichloro-2-propanol with S9 mix. Esters of both chlorohydrines with fatty acids has smaller mutagenic effects than unesterified compounds.

Sodium azide-induced mutagenesis in Saccharomyces cerevisiae.

Sodium azide (0.5--2.0 X 10(-5) M), applied for 24 h on cells growing in complete medium, increased up to 26 times the frequency of reversions and locus-specific suppressor mutations of allele ilv1-92 in diploid strain D7 of Saccharomyces cerevisiae. Similarly, it enhanced the frequency of reversions and/or mitotic gene conversions of alleles trp5-12/trp5-27 up to 19 times. Reconstruction experiments showed that the increase of mutations in complete medium was not due to a selection of prototrophic types under growth conditions and, therefore, that sodium azide acts as a weak mutagen in S. cerevisiae under growth conditions at a low pH. No mutagenic or convertogenic effect was observed when azide was applied to resting cells in buffer at pH 4.2.

Mutagenesis of Saccharomyces cerevisiae by sodium azide activated in barley.

Concentrated dialysate of the extract prepared from barley seeds treated with sodium azide increased up to 100--200 times the frequency of forward mutations to cycloheximide resistance in the excision-deficient UV-sensitive heploid strain rad2-5 of Saccharomyces cerevisiae, when applied to growing cells in complete medium at pH 4.2. Only a slight increase of mutation frequency (less than 4 times) was found in the haploid RAD+ strain treated in the same way as well as in haploid RAD+ and rad2-5 strains treated directly by sodium azide. In contrast with the barley-activated sodium azide, UV irradiation was more effective in the induction of cycloheximide resistance in the RAD+ strain than in the RAD2-5 mutant. The dialysate from azide-treated barley seeds, applied at both pH 4.2 and pH 9, also significantly increased the frequency of locus-specific suppressor mutations to isoleucine independence and -- to a lesser extent -- reversions and/or gene conversions in the trp5 locus in growing cells of the diploid strain D7. The dialysate was also mutagenic in resting cells of strains D7 and rad2-5 but with lower effectiveness.

The effect of ultrasound and its combination with radiation on the genetic material of Saccharomyces cerevisiae.

Ultrasonication at 20 kHz, intensity 35 W/cm2 and amplitude 15--25 micron of a diploid strain of Saccharomyces cerevisiae was found to act as a weak mutagen with maximum efficiency at the 20% survival of the cells. Under these conditions, the frequency of reversion of the suppressible allel ilv1-92 increased ten times, the frequency of mitotic gene conversion four times. Doses leading to survivals lower than 20% led to a slight increase in the frequency of cytoplasmic respiration-deficient mutants. Submutagenic doses applied immediately after gammaradiation or UV light did not substantially increase the effect of these physical agents on the genetic material of the yeast strain investigated. Application of ultrasound prior to UV radiation did not considerably influence the effect of the radiation either.