Evidence for regulation of protein synthesis at the elongation step by CDK1/cyclin B phosphorylation

Eukaryotic elongation factor 1 (eEF-1) contains the guanine nucleotide exch ange factor eEF-1B that loads the G protein eEF-1A with GTP after each cycl e of elongation during protein synthesis. Two features of eEF-1B have not y et been elucidated: (i) the presence of the unique valyl-tRNA synthetase; ( ii) the significance of target sites for the cell cycle protein kinase CDK1 /cyclin B, The roles of these two features were addressed by elongation mea surements in vitro using cell-free extracts. A poly(GUA) template RNA was g enerated to support both poly(valine) and poly(serine) synthesis and poly(p henylalanine) synthesis was driven by a poly(uridylic acid) template, Elong ation rates were in the order phenylalanine > valine > serine, Addition of CDK1/cyclin B decreased the elongation rate for valine whereas the rate for serine and phenylalanine elongation was increased, This effect was correla ted with phosphorylation of the eEF-1 delta and eEF-1 gamma subunits of eEF -1B, Our results demonstrate specific regulation of elongation by CDK1/cycl in B phosphorylation.