Drosophila Translational Elongation Factor-1γ Is Modified in Response to DOA Kinase Activity and Is Essential for Cellular Viability

Abstract

Abstract Drosophila translational elongation factor-1γ (EF1γ) interacts in the yeast two-hybrid system with DOA, the LAMMER protein kinase of Drosophila. Analysis of mutant EF1γ alleles reveals that the locus encodes a structurally conserved protein essential for both organismal and cellular survival. Although no genetic interactions were detected in combinations with mutations in EF1α, an EF1γ allele enhanced mutant phenotypes of Doa alleles. A predicted LAMMER kinase phosphorylation site conserved near the C terminus of all EF1γ orthologs is a phosphorylation site in vitro for both Drosophila DOA and tobacco PK12 LAMMER kinases. EF1γ protein derived from Doa mutant flies migrates with altered mobility on SDS gels, consistent with it being an in vivo substrate of DOA kinase. However, the aberrant mobility appears to be due to a secondary protein modification, since the mobility of EF1γ protein obtained from wild-type Drosophila is unaltered following treatment with several nonspecific phosphatases. Expression of a construct expressing a serine-to-alanine substitution in the LAMMER kinase phosphorylation site into the fly germline rescued null EF1γ alleles but at reduced efficiency compared to a wild-type construct. Our data suggest that EF1γ functions in vital cellular processes in addition to translational elongation and is a LAMMER kinase substrate in vivo.