Nucleotide sequences from messenger RNA transcribed from the operator-proximal portion of the tryptophan operon of Escherichia coli

³²P-labeled messenger RNA transcribed in vivo from the operator-proximal portion of the tryptophan operon of Escherichia coli was purified by DNA/RNA hybridization. The mRNA preparations obtained were subjected to polyaerylaamide gel electrophoresis, and a number of discrete labeled bands were detected. Characterization of the labeled bands and of purified, unbanded mRNA preparations, by partial sequence analysis of the oligonucleotides obtained following T₁ and pancreatic RNase digestion, revealed that the bands represented discrete segments of the trp mRNA molecule. This observation suggests that endonucleolytic cleavage occurs in vivo at specific sites in the mRNA molecule.