TRANSALDOLASE MUTANTS IN THE YEAST KLUYVEROMYCES-LACTIS PROVIDE EVIDENCE THAT GLUCOSE CAN BE METABOLIZED THROUGH THE PENTOSE-PHOSPHATE PATHWAY

We have isolated the gene encoding transaldolase from Kluyveromyces la ctis (KITAL1) by screening a genomic library of this yeast using the T AL1 gene of Saccharomyces cerevisiae as a radioactive probe. The clone isolated contained an open reading frame of 1002bp, encoding a protei n with 76% identical residues in the deduced amino acid sequences as c ompared to Tal from S. cerevisiae. KITAL1 can complement a tall deleti on of S. cerevisiae for enzymatic activity. The transcription start of KITAL1 was located at -69 bp relative to the ATG translation start co don. Deleting a large part of the open reading frame from the genome d id not lead to any obvious phenotype. Transaldolase was not produced i n such mutants as shown by immunological detection. In combination wit h a double null-mutant in the genes encoding the phosphofructokinase s ubunits in K. lactis (Klpfk1 Klpfk2 Kltal1), the cells lost their abil ity to grow on glucose. We take this as strong evidence that glucose i s metabolized via the pentose phosphate pathway in this yeast when gly colysis is blocked. In addition, by tetrad analysis we detected a clos e linkage to KIPFK1 and inferred that KITAL1 is localized on chromosom e 1.