pepB gene which encodes peptidase B was mapped at 54 min on the Escherichia coil K-12 linkage map. pepB was cloned and its nucleotide sequence was determined. pepB gene has an open reading frame which encodes a protein of 420 amino acid residues the molecular weight of which Is estimated to be 45,666. Peptidase B was suggested to be a homohexamer. The deduced amino acid sequence of peptidase B has an absolutely conserved octapeptide, NTDAEGRL, known as a zinc/manganese binding site and a so-called cytosol aminopeptidase signature in its central region. Peptidase B was suggested to belong to the peptidase family M17.