The amino acid sequence of rat ribosomal protein S16 was deduced from the sequence of nucleotides in a recombinant cDNA and confirmed from the NH2-terminal amino acid sequence of the protein. S16 contains 145 amino acids (the NH2-terminal methionine is removed after translation of the mRNA) and has a molecular mass of 16,304. Hybridization of the cDNA to digests of nuclear DNA suggests that there are 11-13 copies of the S16 gene. The mRNA for the protein is about 700 nucleotides in length. Rat S16 is homologous to mouse S16 (there are 2 amino acid changes and a residue is deleted) and related to Halobacterium morismortui ribosomal protein S3 and to Escherichia coli S9.