A structural and phylogenetic study of the HO gene from Saccharomyces bayanus var. uvarum.

A novel HO gene (Uv-HO) was cloned from the Saccharomyces bayanus var. uvarum (abbreviated as S. uvarum in this study) type strain. The coding region of Uv-HO showed relatively high homology (95%) to that of the Sb-HO gene (S. bayanus var. bayanus HO), but not to the HO genes of other Saccharomyces sensu stricto species. However, the 5' and 3' non-coding region of Uv-HO showed less similarity (79% and 76% respectively) even to those of the most homologous gene Sb-HO. Motifs of the mating-type control and the cell-cycle control were conserved in the 5' non-coding region of Uv-HO, but numbers and positions of motifs were different from those of Sb-HO. CHEF-Southern analysis showed that all tested strains of S. bayanus species, including S. uvarum, carried the HO gene on the 1,100-kb chromosome. By HO-typing PCR using mixed primers, which provided a rapid and convenient tool for yeast identification, either the Uv-HO gene or the Sb-HO gene was detected in strains of S. bayanus species, but two strains were found to have both types of HO gene in each genome. These results suggest that S. uvarum has a unique sequence, but might share the same chromosome constitution within S. bayanus species, and that S. bayanus is a heterogeneous species, of which some strains might be natural hybrid.