The nucleotide sequence of gene araA of Salmonella typhimurium LT2 has been determined. The gene encodes an L-arabinose isomerase (EC 5.3.1.4) of 500 amino acid residues with a calculated Mr of 55814. The ATG start codon of araA is 10 bp distal to the TAA termination codon of araB. A presumed ribosome-binding site (RBS) "TAAGGA" 7 bp from the ATG codon overlaps the stop codon of araB. L-Arabinose isomerase was purified and the amino acid composition is in agreement with that predicted from the DNA sequence. The NH2-terminus of the protein is modified as the sequence cannot be analyzed by the automated Edman degradation. Amino acid composition analyses of both NH2-terminal and C-terminal cyanogen bromide (CNBr) cleaved peptides and partial amino acid sequence of the C-terminal peptide are consistent with the deduced amino acid sequence.