High impact information on SIP1

• The SIP1 protein co-immunoprecipitated with SNF1 and was phosphorylated in vitro [1].
• Previous studies showed that the Sip1/Sip2/Gal83 component plays a structural role in the complex [2].
• Cyclic AMP-dependent protein kinase regulates the subcellular localization of Snf1-Sip1 protein kinase [3].
• The Sip1 beta subunit resides in the cytosol in glucose-grown cells and relocalizes to the vacuolar membrane in response to carbon stress [3].
• We show that translation of Sip1 initiates at the second ATG of the open reading frame, yielding a potential site for N myristoylation, and that mutation of the critical glycine abolishes relocalization [3].

Biological context of SIP1

• We have carried out in vivo studies of the genetic and carbon control of Sip1p phosphorylation [4].
• SIP1 is a catabolite repression-specific negative regulator of GAL gene expression [5].
• Increased gene dosage of SIP1 rescued the ethanol growth defect observed in cells expressing Sip1 as their only beta subunit and increased the in vitro activity of Snf1 kinase purified from these cells [6].
• DNA sequence analysis revealed that they were orthologues of the yeast GAL83/SIP1/SIP2 genes and their mammalian counterparts, AMPK beta-subunits [7].
• The Snf1 catalytic subunit also exhibits aberrant localization to the vacuolar membrane in PKA-deficient cells, indicating that PKA regulates the localization of Snf1-Sip1 protein kinase [3].

Associations of SIP1 with chemical compounds

• High-copy clones of SIP1 and SIP2 cross-complement the GAL83-2000 mutation (as well as GAL82-1, a mutation in another gene involved in glucose repression), suggesting that these four genes may perform similar functions in glucose repression [8].
• We further show that the cyclic AMP-dependent protein kinase (protein kinase A [PKA]) pathway maintains the cytoplasmic localization of Sip1 in glucose-grown cells [3].

Physical interactions of SIP1

• These results reveal new complexities in carbon response signaling, and may reflect the involvement of the Sip1 protein in the same complex as the Mig1 and Ssn6 proteins [4].
• Examination of the protein composition of the purified Snf1 enzyme complexes indicated that the Sip1 protein was present in substoichiometric levels [6].

Regulatory relationships of SIP1

• Metabolic labeling reveals phosphorylation of Sip1p under both carbon catabolite-repressing and non-repressing conditions and in both SNF1 wild-type and snf1-deletion cells [4].

Other interactions of SIP1

• The Sip1 protein is known to undergo phosphorylation when associated in vitro with the Snf1 protein kinase [4].
• We have isolated the SIP1 gene as a multicopy suppressor of the gal83-associated defect in glucose repression of GAL gene expression [5].
• Evidence indicates that Sip1 and Sip2 do not interact with Sip4 [2].

Analytical, diagnostic and therapeutic context of SIP1

• Western blots revealed that Sip1p abundance is not markedly affected by carbon source, suggesting that Sip1p may be regulated post-translationally [5].

References