The DNA sequence of the part of the Mycoplasma capricolum genome that contains the genes for 20 ribosomal proteins and two other proteins has been determined. The organization of the gene cluster is essentially the same as that in the S10 and spc operons of Escherichia coli. The deduced amino acid sequence of each protein is also well conserved in the two bacteria. The G + C content of the M. capricolum genes is 29%, which is much lower than that of E. coli (51%). The codon usage pattern of M. capricolum is different from that of E. coli and extremely biased to use of A and U(T): about 91% of codons have A or U in the third position. UGA, which is a stop codon in the "universal" code, is used more abundantly than UGG to dictate tryptophan.