Identification of a novel gene controlling homothallism in the yeast Kazachstania naganishii isolated in Japan.

Abstract

A novel gene controlling homothallic life cycle was identified in the yeast Kazachstania naganishii isolated in Japan. This gene was isolated by means of complementing a mutation, mti1, which had led to heterothallism from original homothallism in the yeast. The configuration of original mutation in MTI1 gene revealed that a truncated product is formed due to occurrence of a stop codon by a nucleotide insertion. When the gene was disrupted with a marker, the disruptant spore clone was haploid and stably heterothallic. Disfunction of the gene caused inability to self-diploidize due to defect of mating-type interconversion. The gene MTI1 (for Mating Type Interconversion) is a weak homolog of the Saccharomyces cerevisiae VID22/ENV11, which has been reported to function in vacuolar protein processing. K. naganishii has a gene representing significant homology with the HO gene of S. cerevisiae on chromosome V, which has not been clarified to be involved in regulation of life cycle in K. naganishii. The MTI1 gene defined in this study is located on K. naganishii chromosome IV and does not represent significant homology to the above ScHO-like gene and any other genes concerning life cycles of yeasts. From the viewpoint of gene evolution, it is extremely interesting that the MTI1 gene is a new type of gene controlling homothallism in addition to an HO-type gene, leading to discovery of an unknown mechanism regulating life cycles in yeasts.