The complete nucleotide sequence of a 179-nucleotide precursor (p5A) of 5 S ribosomal RNA from Bacillus subtilis is presented. In addition to the 116-nucleotide mature segment, the p5A molecule contains 21 additional nucleotides at its 5' end and 42 at its 3' terminus. Structural features within the p5A molecule which possibly interact with a specific maturation endonuclease (RNase M5) are identifiable. These include 2-fold rotational symmetry about the cleavage sites, which may approximately place the p5A molecule on the RNase M5 surface, and translational (positional) symmetry, which may precisely orient substrate phosphodiester bonds with respect to catalytic amino acids. Certain features of the 3' -terminal, precursor-specific portion of p5A possibly are involved in the termination of DNA transcription.