Two rat recombinant cDNAs were characterized; they encode fusion proteins that have at their NH2 terminus the conserved 76 amino acid ubiquitin and at their carboxyl terminus the extension ribosomal proteins S27a (SO amino acids and a molecular weight of 9,397) or L40 (52 amino acids and a molecular weight of 6,177). The fusion proteins are processed in a reticulocyte lysate to ubiquitin and either S27a or L40. Hybridization of cDNAs to digests of nuclear DNA suggests that there are 14 to 19 copies of the S27a, and 6 to 10 of the L40, genes. The mRNA for ubiquitin-S27a has about 700 nucleotides and ubiquitin-L40 about 650. Ribosomal proteins S27a and L40 contain zinc finger motifs of the C-2-C-2 variety. S27a and L40 are related to ribosomal proteins from other species. (C) 1995 Academic Press, Inc.