MCK1, A MEMBER OF THE GLYCOGEN-SYNTHASE KINASE-3 FAMILY OF PROTEIN-KINASES, IS A NEGATIVE REGULATOR OF PYRUVATE-KINASE IN THE YEAST SACCHAROMYCES-CEREVISIAE

An interaction between the Saccharomyces cerevisiae protein kinase Mck 1 and pyruvate kinase (Pyk1) was detected by using the two-hybrid meth od. Purified Mck1 was able to phosphorylate purified Pyk1 on Ser in vi tro. Pyruvate kinase activity was elevated in mck1 Delta cells. Severa l of the phenotypes of mck1 Delta mutants are similar to those observe d in cells overexpressing PYRI. Co-overexpression of MCK1 suppressed a ll of the phenotypes associated with PYK1 overexpression. These result s indicate that Mck1 negatively regulates pyruvate kinase activity, po ssibly by direct phosphorylation.