The guanine‐nucleotide‐exchange Complex (EF‐1βγδ) of Elongation Factor‐1 Contains two Similar Leucine‐Zipper Proteins EF‐1δ, p34 Encoded by EF‐1δ1 and p36 Encoded by EF‐1δ2

We have cloned and sequenced a Xenopus cDNA referred to as EF‐1δ2. The cDNA is homologous to EF‐1δ1 encoding for EF‐1δ a protein of the guanine‐nucleotide exchange complex of elongation factor‐1 (EF‐1). The protein sequence deduced from the cDNA, contains the two characteristic features of EF‐1δ protein, the leucine‐zipper domain and the guanine‐nucleotide exchange domain. In vitro and in vivo translation leads to the production of a 36‐kDa protein from EF‐1δ2 and a 34‐kDa protein from EF‐1δ1. The clone EF‐1δ2 therefore encodes for authentic p36 protein of EF‐1βγδ complex, while EF‐1δ1 encodes for a newly characterised p34 protein of the leucine zipper family. Both EF‐1δ proteins are simultaneously present in oocytes extracts, at a molecular ratio around 1:10 for p34 versus p36 proteins. Both are associated in a macromolecular structure that is greater than 750 kDa upon gel filtration. The two proteins are targets for Cdc2 kinase in meiotic maturation.