Cycloheximide-resistant Mutants Research Articles

Biochemical genetic studies of cycloheximide resistance in Neurospora crassa.

Genetic analysis of a number of cycloheximide-resistant mutants of Neurospora crassa has shown that resistance is controlled by several genes. Two of these appear to be located on linkage group V. Resistance to the antibiotic is dominant in wild-type-mutant heterokaryons. Two types of cycloheximide-resistant mutants were isolated: one type exhibited colonial morphology only when grown in the presence of cycloheximide and the other type maintained normal morphology even at high concentrations of the antibiotic. Reconstitution experiments with supernatant solutions and 80S monosomes prepared from wild-type and resistant mutant strains indicated that the property of cycloheximide resistance most likely is associated with the ribosomes. No electrophoretic or serological differences were found between the ribosomal proteins of the wild-type and resistant mutants.

Inheritance of Sex in Achlya bisexualis

Parental crosses, backcrosses, repeated backcrosses, and sib matings with several strains of Achlya bisexualis Coker and Couch have been made. Progeny were tested for sexual reaction with the parental strains. The distribution of sex observed could not be explained on the basis of any simple gene or chromosomal mechanism. Two factors were suggested which may affect the distribution of sex. They are selfing in the female and the complexity of the hormonal system which controls the expression of sex. The inheritance of a cycloheximide-resistant mutant argues against selfing; however, further studies with other genetic markers are needed.

Evidence for Diploidy inAchlya BisexualisBased on Inheritance of Cycloheximide Resistance

In a study of a cycloheximide-resistant mutant of the oomycete Achlya bisexualis Coker & Couch two important observations have been made. The first concerns the inheritance of cycloheximide resistance and the second is the position of meiosis in the life cycle of this organism. Induced cycloheximide-resistant mutants are known in several species of fungi. The inheritance of cycloheximide resistance in Saccharomyces cerevisiae Hansen was shown to be controlled by six genes, four of which were dominant and two recessive (Wilkie and Lee, 1965). Additional modifier genes were also hypothesized. In both Physarum polycephalum Schw. (Haugli et al., 1972) and Neurospora crassa Shear & Dodge (Hsu, 1963) resistance was shown to be controlled by two loci. In

Evidence for Diploidy in Achlya bisexualis Based on Inheritance of Cycloheximide Resistance

SUMMARYStudy of a UV-induced cycloheximide-resistant mutant of Achlya bisexualis indicates that the mutant is homozygous dominant for cycloheximide resistance. The results support the hypothesis that Achlya is diploid and that meiosis occurs in the gametangia.

Genetics and biochemistry of cycloheximide resistance in Physarum polycephalum.

Cycloheximide-resistant mutants of Physarum polycephalum were induced in the haploid myxamoebae by the combined action of UV1 and caffeine (Haugli and Dove, 1972) or by treatment with NMG2. Eight independent mutants segregated in a Mendelian fashion (Table 1). Crosses between 6 of the mutants revealed 2 loci, actA and actB, for cycloheximide resistance (Table 2).

Characteristics of TCA Cycle of Cycloheximide-resistant Mutant ofZygosaccharomyces soja

Glucose catabolism inZygosaccharomyces sojawas carried out through fermentation, whereas riboflavin producing mutant obtained by cycloheximide treatment was found to utilize oxidative mechanisms. For instance, growth of mutant was sustained in minimal medium containing TCA cycle intermediates as the sole carbon source, whereas the mother strain could not grow on such culture media. Furthermore, malonate inhibited the oxidation of succinate with resting cells of mutant. As these results support the existence of TCA cycle in mutant, various enzyme activities relating to TCA cycle were investigated by the use of cell-free extracts of both strains. Aconitase, α-ketoglutaric decarboxylase, succinic dehydrogenase, fumarase, isocitritase and glyoxylic reductase were not detected in mother strain. These data indicated that both the TCA cycle and glyoxylate cycle did not operate in mother strain. On the other band, all enzyme activities relating to TCA cycle and glyoxylate cycle were verified in mutant. This finding indicates that both the TCA cycle and glyoxylate cycle performed a main role in carbohydrate catabolism in mutant. The evidence that alteration of the mode of glucose catabolism from fermentation in case of mother strain to respiration of mutant elicited by the action of cycloheximide was thus explained.