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Three different alleles of the β-isopropylmalate dehydrogenase gene were cloned and sequenced from a leucine auxotrophic mutant, G587, of Candida maltosa. The cloning of functionally-intact wild-type genes from this mutant strain suggests the presence of silent gene copies. An interallelic-divergence comparison has provided evidence for new regulatory mechanisms. Sequence data and karyotype analysis argue for a highly-aneuploid genome of C. maltosa. An interpretation for the spontaneous auxotrophy-prototrophy-auxotrophy sequence of mutations in C. maltosa is suggested. [ABSTRACT FROM AUTHOR]

The usefulness of hybridization by protoplast fusion and mitotic segregation for the genetic analysis of the imperfect fodder yeast Candida maltosa was tested. Mitotically stable fusion hybrids were obtained with frequencies between 10 and 10. Complementation tests were performed by protoplast fusion. Substances that are known to induce frequent mitotic segregation in other yeast species such as benomyl, p-fluorophenylalanine, and acriflavine were ineffective in C. maltosa. UV irradiation induced mitotic segregation in up to 10%. This agent induced mainly mitotic crossing over in C. maltosa. Our data enabled the construction of the linkage group I with the sequence CEN-ade-26- pro-1. [ABSTRACT FROM AUTHOR]

Nicotinic acid in Rhodotorula glutinis is synthesized from tryptophan via N′-formyIkynurenine, kynurenine, 3-hydroxykynurenine and 3-hydroxyanthranilic acid. Auxotrophic mutants, with blocked synthesis at various steps between tryptophan and 3-hydroxyanthranilic acid, can grow with 100 μg/ml anthranilic acid (concentration in the agar-agar). The usually required concentration of substances such as nicotinic acid or other substances after the blocked step is about 2 μg/mI. Auxotrophs with a block between 3-hydroxyanthranilic acid and nicotinic acid are not able to grow with anthranilic acid. Therefore mutants requiring nicotinic acid with a blocked step between tryptophan and 3-hydroxyanthranilic acid can synthesize nicotinic acid from anthranilic acid, a substance formed in the first step of tryptophan synthesis from chorismic acid, by eluding the blocked pathways The same ability has been found in prototroph revertants with the original block of the auxotrophs but with a second mutation in the gene of anthranilate synthetase. As a result of this mutation the feedback inhibition by tryptophan is disturbed and anthranilic acid is produced in excess. When the culture medium of the prototrophs is analysed by paper chromatography after adding anthranilic acid to the growing culture, 3-hydroxyanthranilic acid as one of the formed products can be found. Summarizing these facts it is evident, that there exists a "short-cut"-pathway of nicotinic acid synthesis in Rh. glutinis, which is realized by direct hydroxylation of anthranilic acid to 3-hydroxyanthranilic acid. This "short-cut"pathway however is only possible, when anthranilic acid in the cell is present in excess. [ABSTRACT FROM AUTHOR]