Nucleotide sequence of the xth gene of Escherichia coli K-12.

The xth gene of Escherichia coli K-12, which encodes exonuclease III, has been sequenced. Exonuclease III from a cloned copy of the E. coli K-12 gene has been purified and characterized. The molecular weight (30,921), the amino-terminal amino acid sequence, and the amino acid composition of the polypeptide predicted from the nucleotide sequence are in excellent agreement with those properties determined for the purified enzyme. The xth promoter was mapped by primer extension of in vivo transcripts. Inspection of the nucleotide sequence reveals that a region of dyad symmetry which could form a hairpin stem-loop structure in RNA characteristic of a rho-dependent terminator lies immediately downstream from the xth gene.