The nucleotide sequences have been determined for the promoter regions of two ribosomal RNA operons, rrnA and rrnE, in E. coli. The sequences cover the two in vitro transcription start sites identified for each operon (Gilbert, der Boer and Nomura, 1979). The first two start sites are 283 and 291 bp preceding the mature 16S rRNA (m16S rNA) coding regions for rrnE and rrnA, respectively; the second start sites are 174 and 174 +/- 1 bp preceding the m16S rRNA coding regions for rrnE and rrnA, respectively. Each of these start sites has an identifiable "Pribnow box" sequence 6-7 bp upstream from the start site. The nucleotide sequences of the two operons have nearly complete homology from the m16S rRNA coding regions to positions 145 bp upstream from those regions, and at the regions surrounding the Pribnow boxes preceding the first start sites. The DNA sequences indicate that the RNAs transcribed from the first start sites of rrnE and rrnA are quite different in their first 150 nucleotides. These heterogeneous regions, however, precede the RNAse III cleavage sites (deduced previously by Young and Steitz, 1978), and the "precursor 16S rRNA" molecules are largely homogeneous. The nucleotide sequences of the promoter regions of the two rRNA operons are also compared with those or rrnD and rrnX, determined by Young and Steitz (1979), and some common features are discussed.