The Snf1 protein kinase and its activating subunit, Snf4, interact with distinct domains of the Sip1/Sip2/Gal83 component in the kinase complex.
The Snf1 protein kinase plays a central role in the response to glucose starvation in the yeast Saccharomyces cerevisiae. Previously, we showed that two-hybrid interaction between Snf1 and its activating subunit, Snf4, is inhibited by high levels of glucose. These findings, together with biochemical evidence that Snf1 and Snf4 remain associated in cells grown in glucose, suggested that another protein (or proteins) anchors Snf1 and Snf4 into a complex. Here, we examine the possibility that a family of proteins, comprising Sip1, Sip2, and Gal83, serves this purpose. We first show that the fraction of cellular Snf4 protein that is complexed with Snf1 is reduced in a sip1delta sip2delta gal83delta triple mutant. We then present evidence that Sip1, Sip2, and Gal83 each interact independently with both Snf1 and Snf4 via distinct domains. A conserved internal region binds to the Snf1 regulatory domain, and the conserved C-terminal ASC domain binds to Snf4. Interactions were mapped by using the two-hybrid system and were confirmed by in vitro binding studies. These findings indicate that the Sip1/Sip2/Gal83 family anchors Snf1 and Snf4 into a complex. Finally, the interaction of the yeast Sip2 protein with a plant Snf1 homolog suggests that this function is conserved in plants.
Jiang
R
R
Department of Genetics and Development, Columbia University, New York, New York 10032, USA.
Carlson
M
M
D055372:AMP-Activated Protein Kinases; D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics; D002352:Carrier Proteins; D017124:Conserved Sequence; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D002352:Carrier Proteins; D005656:Fungal Proteins; C085569:GAL83 protein, S cerevisiae; D010940:Plant Proteins; D012097:Repressor Proteins; C091267:SIP2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D011494:Protein Kinases; C071570:SNF1-related protein kinases; D017346:Protein Serine-Threonine Kinases; C075934:SIP1 protein, S cerevisiae; C078651:SNF4 protein, S cerevisiae; D055372:AMP-Activated Protein Kinases; D005947:Glucose