The sequence of almost 700 nucleotides encompassing the gene for ribosomal protein S20 of Escherichia coli has been determined using the chemical technique of Maxam and Gilbert (Maxam, A. M., and Gilbert, W. (1977) Proc. Natl. Acad. Sci. U. S. A. 74, 560-564). Comparison of this sequence with that of known bacterial promoters reveals two promoter-like sequences whose putative initiation sites for transcription lie 132 ("site 1") and 42 ("site 2") base pairs to the 5' side of the coding sequence. Partial digestion experiments demonstrate that RNA polymerase is capable of binding to and protecting both of these sites from DNase 1 digestion, consistent with their functioning as promoters. Interestingly, site 1 is more compact that any previously described bacterial promoter. A second feature of the sequence is the presence of UUG as the translational initiation codon. Finally, the nucleotide sequence supports the hypothesis (Jue, R. A., Woodbury, N. W., and Doolittle, R. F. (1980) J. Mol. Evol. 15, 129-148) that S20 is composed of three tandemly repeated domains.