Cloning and sequence analysis of tryptophan synthetase genes of an extreme thermophile, Thermus thermophilus HB27: plasmid transfer from replica-plated Escherichia coli recombinant colonies to competent T. thermophilus cells

Tryptophan synthetase genes (trpBA) of the extreme thermophile Thermus thermophilus HB27 were cloned by a novel method of direct plasmid transfer from replica-plated Escherichia coli recombinant colonies to competent T. thermophilus HB27 trpB cells. The nucleotide sequences of the trpBA genes were determined. The amino acid sequences deduced from the nucleotide sequences of Thermus trpB and trpA were found to have identities of 54.8 and 28.7%, respectively, with those of E. coli trpB and trpA genes. Low cysteine content (one in trpB; zero in trpA) is a striking feature of these proteins, which may contribute to their thermostability.