GENETIC AND BIOCHEMICAL-EVIDENCE FOR YEAST GCN2 PROTEIN-KINASE POLYMERIZATION

The GCN2 (general control kinase 2) protein is an eIF2-alpha (eukaryot ic initiation factor a) kinase which mediates translational derepressi on of the yeast general control transcriptional activator, GCN4, upon amino-acid starvation. We isolated and characterized GCN2 mutations di fferentially affecting GCN2 function. Mutations mapping in, or close t o, the ATP-binding site of the kinase moiety result in constitutively activated GCN2 molecules. A C-terminal regulatory mutation dramaticall y affects translation initiation rates resulting in pleiotropic phenot ypes. The effect of mutations in both regions were found to depend on eIF2-alpha phosphorylation. We have demonstrated that GCN2 mutants hav e altered autophosphorylation activities in vitro, depending on the pr esence or absence of a wild-type GCN2 gene and that GCN2 elutes in gel -filtration chromatography fractions with high apparent molecular mass . Both these genetic and biochemical findings suggest that GCN2 functi oning might involve polymerization to form dimers or tetramers.