Search

Gene conversions are nonreciprocal sequence exchanges between genes. They are relatively common in Saccharomyces cerevisiae, but few studies have investigated the evolutionary fate of gene conversions or their functional impacts. Here, we analyze the evolution and impact of gene conversions between the two genes encoding 2-deoxyglucose-6-phosphate phosphatase in S. cerevisiae, Saccharomyces paradoxus and Saccharomyces mikatae. Our results demonstrate that the last half of these genes are subject to gene conversions among these three species. The greater similarity and the greater percentage of GC nucleotides in the converted regions, as well as the absence of long regions of adjacent common converted sites, suggest that these gene conversions are frequent and occur independently in all three species. The high frequency of these conversions probably result from the fact that they have little impact on the protein sequences encoded by these genes.

A study of the genus Saccharomyces by new biocharacters demonstrates indirectly the genotype of each species; intracellular osidases (lactose - maltose -cellobiase - melibiase - invertase - trehalase) and vitamin requirements (biotin-folic acid-inositol-niacine-pantothénate-para-aminobenzoic acid-pyridozine-thiamine) reveal some phylogenetic links between the species. It appears that Van der Walt's group I is very homogeneous and must be restricted to only 7 species. The torulospora group seems very similar to the genus Debaryomyces when vitamin needs and osidases are considered; the relations between the 2 groups are discussed. When other biocharacters are studied (nitrite reductase-immunological properties, etc. ...) the value in the GC content (4-5% lower in Debaryomyces) will be established. These results confirm that intracellular oxidases and vitamin needs are very valuable tools for systematic criteria.