CHARACTERIZATION OF A GLUCOSE-REPRESSED PYRUVATE-KINASE (PYK2P) IN SACCHAROMYCES-CEREVISIAE THAT IS CATALYTICALLY INSENSITIVE TO FRUCTOSE-1,6-BISPHOSPHATE

We have characterized the gene YOR347e of Saccharomyces cerevisiae and shown that it encodes a second functional pyruvate kinase isoenzyme, Pyk2p. Overexpression of the YOR347c/PYK2 gene on a multicopy vector r estored growth on glucose of a yeast pyruvate kinase 1 (pyk1) mutant s train and could completely substitute for the PYK1-encoded enzymatic a ctivity. PYK2 gene expression is subject to glucose repression. A pyk2 deletion mutant had no obvious growth phenotypes under various condit ions, but the growth defects of a pyk1 pyk2 double-deletion strain wer e even more pronounced than those of a pyk1 single-mutation strain. Py k2p is active without fructose-1,6-bisphosphate. However, overexpressi on of PYK2 during growth on ethanol did not cause any of the deleterio us effects expected from a futile cycling between pyruvate and phospho enolpyruvate. The results indicate that the PYK2-encoded pyruvate kina se may be used under conditions of very low glycolytic flux.