Nucleotide sequence of the trpB gene in Escherichia coli and Salmonella typhimurium

We have obtained the entire nucleotide sequence of the penultimate gene of the tryptophan operon, trpB, in Escherichia coli and Salmonella typhimurium. The amino acid sequence deduced for the E. coli gene product is in agreement with earlier, fragmentary protein sequence results. The trpB nucleotide sequences for the two bacterial species are perfectly colinear and show 85% identity. Most of the nucleotide differences found are without consequence for the amino acid sequence, which shows greater than 96% identity. The degree of conservation of both the nucleotide and amino acid sequences is significantly greater than for trpA, the adjacent gene encoding the other subunit of the same enzyme. When synonymous third codon position nucleotide differences are examined, they seem to be distributed at random throughout trpB and trpA, except for one completely conserved 66 basepair long region within trpB.