EF-1 (elongation factor-1) is a multi-protein complex that is responsible for the delivery of aminoacyl-tRNAs to the ribosome. The EF-1 protein complex is composed of four subunits: EF-1 alpha, EF-1 beta, EF-1 delta and EF-1 gamma . EF-1 beta is a 225 amino acid member of the EF-1 beta/EF-1 delta protein family and contains one GST C-terminal domain. Both EF-1 beta and EF-1 delta stimulate the exchange of GDP bound to EF-1 alpha to GTP. Phosphorylation of EF-1 beta affects the GDP/GTP exchange rate. Alternative splicing events of the gene that encodes EF-1 beta result in three transcript variants that differ only in the 5' UTR.