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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. [ABSTRACT FROM AUTHOR]

Neither exit nor counterflow efflux of thiamin, taken up previously by an active transport, were found in Saccharornyces 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. [ABSTRACT FROM AUTHOR]

Ultrasonication at 20 kHz, intensity 35 W/cm and amplitude 15-25 μm 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 allele 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 γradiation 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. [ABSTRACT FROM AUTHOR]

Six strains of Yarrowia lipolytica tested here were resistant to 10-20 g erythromycin or chloramphenicol per L glycerol-agar medium. Cells tolerating 4 g chloramphenicol per L were very rare and reverted rapidly to the highest resistance. In analogy with Ery mutants of Kluyveromyces lactis, our strains did not grow at 36°C but did not lose their viability at that temperature. Two levels of resistance were found with oligomycin and antimycin A, i.e. 10 and 3 mg/L in the former and 10 and 2 mg/L in the latter. The higher resistance levels segregated mitotically and were, therefore, controlled extrachromosomally. The lower resistance levels showed very frequent changes from sensitivity to resistance that prevented the genetic analysis of this resistance. An almost continuous range of tolerance to <5-400 μg mucidin per L was found in populations of the strains analyzed. Newly formed Muc cells were established only in the presence of the antibiotic. Pure cultures of Muc cells showed an extremely high instability caused by their lower viability and very low growth rate in the absence of mucidin. No loss of resistance to antimycin A was found, although Ant cells revealed similar negative selection. Mutability Muc»Muc and Muc»Muc was higher in Ant cells than in Ant ones. [ABSTRACT FROM AUTHOR]

A reciprocal suppression of rough phenotype was found in rough mutants of two prototrophic strains of Saccharomyces cerevisiae on medium containing 1 % glucose. Suppression affects at least three independent rough loci and is strongly influenced by the genetic background. It is accompanied by suppression of red pigmentation in ade2-1 mutants, and this too responds similarly to the genetic background. There is evidence for at least two independent loci that modify the action of the suppressor of both rough and red. The suppressor segregates regularly and is linked to one of the tested rough loci. It is not a super-suppressor and probably is not involved in the regulatory mechanism of purine biosynthesis either. An involvement of glucose metabolism in the suppression can be assumed from the lifting of the suppression of rough phenotype on lactate medium. [ABSTRACT FROM AUTHOR]

In Saccharomyces cerevisiae a tryptophan requirement suppresses the rough colony phenotype that is produced by mutants at three separate loci. The suppression is strongly influenced by the genetic background and is excercised by both tested tryptophan loci. Very high concentrations of tryptophan in the growth medium relieve the suppression in some segregants. A similar suppression of the rough phenotype was observed in a mutant requiring lysine, while neither histidine nor adenine requirements were effective in that respect. [ABSTRACT FROM AUTHOR]