Primary structures of ribosomal protein YS25 from Saccharomyces cerevisiae and its counterparts from Schizosaccharomyces pombe and rat liver

Protein YS25 and its counterparts, SP-S28 and rat S21 [nomenclature according to Sherton, C. C., & Wool, I. G. (1972) J. Biol. Chem. 247, 4460-4467], from Saccharomyces cerevisiae, Schizosaccharomyces pombe, and rat liver cytoplasmic ribosomes, respectively, were sequenced by a combination of various enzymatic digestions and/or chemical cleavage. Proteins YS25 and SP-S28 consist of 87 amino acid residues, and rat S21 consists of 83. The amino termini are all N alpha-acetylated. The amino-terminal halves of the protein molecules are highly conserved (73-85% homologies) in contrast to the carboxy-terminal parts. Overall, rat S21 is 54% homologous to YS25 and 57% to SP-S28, despite a 76% homology between YS25 and SP-S28. Direct comparison with the available prokaryotic ribosomal protein sequences did not reveal any significant homology.