The cDNA of a previously uncharacterized gene fet5 (factor of eukaryotic transcription, clone no. 5) of the fission yeast Schizosaccharomyces pombe was cloned by the heterospecific complementation of a conditional mutant of Saccharomyces cerevisiae defective in the function of the RNA polymerases I-III common subunit ABC10 beta. The gene encodes a new factor of eukaryotic transcription, Fet5, the first member of a superfamily of proteins for which the area of functioning is determined. The Fet5-superfamily consists of three distinct families of proteins highly evolutionarily conserved and widely spread among eukaryotes. Features of the Fet5 amino acid sequence suggest that it belongs to ATP/GTP-binding proteins.