EF-1C is a component of the aggregate EF-1B, consisting of the subunit forms EF-1A-EF-1C; it was isolated by dissociation of this aggregate in the presence of GTF. The subunit form EF-1C stimulates binding of aminoacyl-tRNA to ribosomes, catalysed by EF-1A, similarly as EF-lßy which stimulates the activity of EF-1 in other eukaryotic cells. EF-1C in the presence of 6 M urea was separated into two polypeptides. Polypeptide of molecular mass 32000 Da is responsible for regeneration of the EF-1A-GTP active complex. Thermal sensitivity of EF-1A was much higher than that of EF-1B, thus a protective role of EF-1C in the EF-1AEF-1C complex is suggested.