MAMMALIAN 5'-AMP-ACTIVATED PROTEIN-KINASE NONCATALYTIC SUBUNITS ARE HOMOLOGS OF PROTEINS THAT INTERACT WITH YEAST SNF1 PROTEIN-KINASE

The 5'-AMP-activated protein kinase is responsible for the regulation of fatty acid synthesis by phosphorylation and inactivation of acetyl- CoA carboxylase. The porcine liver 5'-AMP-activated protein kinase 63- kDa catalytic subunit co-purifies 14,000-fold with a 38- and 4O-kDa pr otein (Mitchelhill, K. I. et al. (1994) J. Biol. Chem. 269, 2361-2364) . The 63-kDa subunit is homologous to the Saccharomyces cerevisiae Snf 1 protein kinase, which regulates gene expression during glucose derep ression. Peptide amino acid and polymerase chain reaction-derived part ial cDNA sequences of both the pig and rat fiver enzymes show that the 38-kDa protein is homologous to Snf4p (CAT3) and that the 40-kDa prot ein is homologous to the Sip1p/Spm/GAL83 family of Snf1p interacting p roteins. Sucrose density gradient and cross-linking experiments with p urified 5'-AMP-activated protein kinase suggest that both the 38- and 40-kDa proteins associate tightly with the 63-kDa catalytic polypeptid e in either a heterotrimeric complex or in dimeric complexes. The 40-k Da subunit is autophosphorylated within the 63-kDa subunit complex. Th e sequence relationships between the mammalian 5'-AMP-activated protei n kinase and yeast Snf1p extend to the subunit proteins consistent wit h conservation of the functional roles of these polypeptides in cellul ar regulation by this family of metabolite-sensing protein kinases.