MULTIPLE PHOSPHORYLATION SITES AND QUATERNARY ORGANIZATION OF GUANINE-NUCLEOTIDE EXCHANGE COMPLEX OF ELONGATION FACTOR-I (EF-1-BETA-GAMMA-DELTA VALRS) CONTROL THE VARIOUS FUNCTIONS OF EF-1-ALPHA/

The eukaryotic guanine-nucleotide exchange factor commonly called elon gation factor-1 beta gamma delta (EF-1 beta gamma delta), comprises fo ur different subunits including valyl-tRNA synthetase (EF-1 beta gamma delta/ValRS). The factor is multiply-phosphorylated by three differen t protein kinases, protein kinase C, casein kinase II and cyclin depen dent kinase 1 (CDK1). EF-1 beta gamma delta/ValRS is organized as a ma cromolecular complex for which we propose a new structural model. Evid ence that EF-1 beta gamma delta/ValRS is a sophisticated supramolecula r complex containing many phosphorylation sites, makes it a potential regulator of any of the functions of its partner EF-1 alpha, not only involved in protein synthesis elongation, but also in many other cellu lar functions.