Analysis of a transketolase gene from Kluyveromyces lactis reveals that the yeast enzymes are more related to transketolases of prokaryotic origins than to those of higher eukaryotes

Abstract

The role of the pentose-phosphate pathway in carbohydrate metabolism of the yeast Kluyveromyces lactis, and the evolutionary relationships between the encoding genes, was investigated. For this purpose, we isolated the gene encoding transketolase (KlTKL1) and determined its nucleotide sequence. Surprisingly, comparisons of the deduced amino-acid sequence with those from other organisms revealed that the yeast enzymes are more related to those from prokaryotic sources than to those from higher eukaryotes. Functional analyses showed that KlTKL1 also complemented a Saccharomyces cerevisiae tkl1 tkl2 double mutant for growth in the absence of aromatic amino acids and restored transketolase activity in this mutant. A band detected in these transformants by Western-blot analysis corresponded to a band detected in K. lactis both in a wild-type strain and in a multicopy transformant with elevated transketolase activity.