CDC2 KINASE SETS A MEMORY PHOSPHORYLATION SIGNAL ON ELONGATION-FACTOREF-1-DELTA DURING MEIOTIC CELL-DIVISION, WHICH PERDURES IN EARLY DEVELOPMENT

EF-1 delta is a physiological substrate for cdc2 protein kinase in Xen opus oocytes The protein is part of the nucleotide exchange factor EF- 1 beta gamma delta, involved in the elongation step of protein synthes is. We show that EF-1 delta exists under four isoforms in the prophase oocyte, all phosphorylable by casein kinase II. Each of the prophase isoforms was further separated into a 36 and a 38 kDa form upon phosph orylation by cdc2 kinase which therefore reveals the existence of eigh t different isoforms. Phosphorylation by cdc2 kinase can be monitored as the electrophoretic mobility dedoublement 36/38 kDa. Developmental regulation of EF-1 delta was analyzed. The cdc2 kinase-induced change occures at meiotic division, after complete oogenesis and perdures dur ing early development. It is therefore a phosphorylation memory signal for early development.