title: Pak1 protein kinase regulates activation and nuclear localization of Snf1-Gal83 protein kinase.
abstract: Three kinases, Pak1, Tos3, and Elm1, activate Snf1 protein kinase in Saccharomyces cerevisiae. This cascade is conserved in mammals, where LKB1 activates AMP-activated protein kinase. We address the specificity of the activating kinases for the three forms of Snf1 protein kinase containing the beta-subunit isoforms Gal83, Sip1, and Sip2. Pak1 is the most important kinase for activating Snf1-Gal83 in response to glucose limitation, but Elm1 also has a significant role; moreover, both Pak1 and Elm1 affect Snf1-Sip2. These findings exclude the possibility of a one-to-one correspondence between the activating kinases and the Snf1 complexes. We further identify a second, unexpected role for Pak1 in regulating Snf1-Gal83: the catalytic activity of Pak1 is required for the nuclear enrichment of Snf1-Gal83 in response to carbon stress. The nuclear enrichment of Snf1 fused to green fluorescent protein (GFP) depends on both Gal83 and Pak1 and is abolished by a mutation of the activation loop threonine; in contrast, the nuclear enrichment of Gal83-GFP occurs in a snf1Delta mutant and depends on Pak1 only when Snf1 is present. Snf1-Gal83 is the only form of the kinase that localizes to the nucleus. These findings, that Pak1 both activates Snf1-Gal83 and controls its nuclear localization, implicate Pak1 in regulating nuclear Snf1 protein kinase activity.
authors.affiliation: Department of Genetics and Development, Columbia University, 701 W. 168th St., HSC922, New York, NY 10032, USA.
authors.forename: Kristina
authors.initials: K
authors.lastname: Hedbacker
authors.forename: Seung-Pyo
authors.initials: SP
authors.lastname: Hong
authors.forename: Marian
authors.initials: M
authors.lastname: Carlson
mesh_terms: D055372:AMP-Activated Protein Kinases; D001483:Base Sequence; D002467:Cell Nucleus / Q000201:enzymology; D004271:DNA, Fungal / Q000235:genetics; D004789:Enzyme Activation; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D005800:Genes, Fungal; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D013912:Threonine / Q000737:chemistry; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D054462:p21-Activated Kinases
chemical_list: D004271:DNA, Fungal; D005656:Fungal Proteins; C085569:GAL83 protein, S cerevisiae; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; C091267:SIP2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D013912:Threonine; C071570:SNF1-related protein kinases; D017346:Protein Serine-Threonine Kinases; C075934:SIP1 protein, S cerevisiae; D054462:p21-Activated Kinases; D055372:AMP-Activated Protein Kinases