Isolation of the Candida albicans histidinol dehydrogenase (HIS4) gene and characterization of a histidine auxotroph.

Genetic studies were done with Candida albicans CBS 562. Various auxotrophs were isolated following mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine. SAG5 (his4C), a stable histidine auxotroph defective in histidinol dehydrogenase activity, was characterized and chosen for further molecular studies. Therefore, the C. albicans HIS4 gene was isolated. The gene was obtained from a genomic library of the wild-type strain, which was constructed in plasmid YEp24. The HIS4 gene was isolated by transformation of a Saccharomyces cerevisiae strain that carried a his4 mutation. The isolated C. albicans HIS4 gene complemented S. cerevisiae his4A, his4B, his4C, and his4ABC mutant strains, which indicates that the clone contains the entire HIS4 gene. The gene was isolated on plasmid pSTC7, whose physical map was constructed with BamHI, SalI, and EcoRV restriction endonucleases, locating the HIS4 gene on a 14-kilobase-pair DNA fragment. Hybridization experiments with HIS4 and C. albicans genomic DNA showed correspondence between the restriction patterns of the gene with that of the chromosomal DNA, indicating that the gene originates from C. albicans and appears in a single copy. Chromosomes of C. albicans CBS562 and four other strains were resolved by orthogonal-field alteration gel electrophoresis. The electrokaryotyping results showed heterogeneity in chromosomal sizes. The electrokaryotyping of CBS 562 showed a resolution of six chromosomal bands, three of which seemed to be doublets. The C. albicans HIS4 gene was located on the largest resolvable chromosome in all of the strains.