title: beta-subunits of Snf1 kinase are required for kinase function and substrate definition.
abstract: The Snf1 kinase and its mammalian homolog, the AMP-activated protein kinase, are heterotrimeric enzymes composed of a catalytic alpha-subunit, a regulatory gamma-subunit and a beta-subunit that mediates heterotrimer formation. Saccharomyces cerevisiae encodes three beta-subunit genes, SIP1, SIP2 and GAL83. Earlier studies suggested that these subunits may not be required for Snf1 kinase function. We show here that complete and precise deletion of all three beta-subunit genes inactivates the Snf1 kinase. The sip1Delta sip2Delta gal83Delta strain is unable to derepress invertase, grows poorly on alternative carbon sources and fails to direct the phosphorylation of the Mig1 and Sip4 proteins in vivo. The SIP1 sip2Delta gal83Delta strain manifests a subset of Snf phenotypes (Raf(+), Gly(-)) observed in the snf1Delta 10 strain (Raf(-), Gly(-)), suggesting that individual beta-subunits direct the Snf1 kinase to a subset of its targets in vivo. Indeed, deletion of individual beta-subunit genes causes distinct differences in the induction and phosphorylation of Sip4, strongly suggesting that the beta-subunits play an important role in substrate definition.
authors.affiliation: Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA. mcs2@pitt.edu
authors.forename: M C
authors.initials: MC
authors.lastname: Schmidt
authors.forename: R R
authors.initials: RR
authors.lastname: McCartney
mesh_terms: D055372:AMP-Activated Protein Kinases; D050976:Basic-Leucine Zipper Transcription Factors; D015153:Blotting, Western; D002455:Cell Division / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism; D000939:Epitopes / Q000737:chemistry; D005656:Fungal Proteins / Q000378:metabolism; D017353:Gene Deletion; D005816:Genetic Complementation Test; D005947:Glucose / Q000494:pharmacology; D006026:Glycoside Hydrolases / Q000378:metabolism; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D010641:Phenotype; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry* / Q000235:genetics*; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators / Q000378:metabolism; D043324:beta-Fructofuranosidase
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D000939:Epitopes; D005656:Fungal Proteins; C085976:MIG1 protein, S cerevisiae; D012097:Repressor Proteins; C099279:SIP4 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; C071570:SNF1-related protein kinases; D017346:Protein Serine-Threonine Kinases; C075934:SIP1 protein, S cerevisiae; D055372:AMP-Activated Protein Kinases; D006026:Glycoside Hydrolases; D043324:beta-Fructofuranosidase; D005947:Glucose