THE GUANINE-NUCLEOTIDE-EXCHANGE COMPLEX (EF-1-BETA-GAMMA-DELTA) OF ELONGATION FACTOR-I CONTAINS 2 SIMILAR LEUCINE-ZIPPER PROTEINS EF-1-DELTA, P34 ENCODED BY EF-1-DELTA(1) AND P36 ENCODED BY EF-1-DELTA(2)

We have cloned and sequenced a Xenopus cDNA referred to as EF-1 delta( 2). The cDNA is homologous to EF-1 delta(1) encoding for EF-1 delta a protein of the guanine-nucleotide exchange complex of elongation facto r-1 (EF-1). The protein sequence deduced from the cDNA, contains the t wo characteristic features of EF-1 delta protein, the leucine-zipper d omain and the guanine-nucleotide exchange domain. In vitro and in vivo translation leads to the production of a 36-kDa protein from EF-1 del ta(2) and a 34-kDa protein from EF-1 delta(1). The clone EF-1 delta(2) therefore encodes for authentic p36 protein of EF-1 beta gamma delta complex, while EF-1 delta(1) encodes for a newly characterised p34 pro tein of the leucine zipper family. Both EF-1 delta proteins are simult aneously 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 pr oteins are targets for Cdc2 kinase in meiotic maturation.