PHOSPHORYLATION OF EIF4E AT A CONSERVED SERINE IN APLYSIA

We have cloned eIF4E from the marine mollusk, Aplysia californica. The sequence of eIF4E from Aplysia is more similar to vertebrate eIF4Es t han to other invertebrate sequences. Aplysia eIF4E is encoded by two t issue-specific RNAs, Antibodies raised to the carboxyl ter minus of eI F4E recognize a 29-kDa protein that can bind to 7-methyl-GTP caps, The phosphorylation site identified in mammalian eIF4E is conserved in th e Aplysia homologue, and an Aplysia eIF4E fusion protein is phosphoryl ated well by both Aplysia protein kinase C isoforms. However, protein kinase C phosphorylates both Ser-207 and Thr-208 in vitro, while only Ser-207 is phosphorylated in vivo. We have confirmed that Ser-207 is p hosphorylated in vivo by raising a phosphopeptide antibody to this sit e. This antibody will be useful in determining the signal transduction pathways leading to eIF4E phosphorylation in Aplysia.