Deletion plasmids from transformants of Pseudomonas aeruginosa trp cells with the RSF1010-trp hybrid plasmid and high levels of enzyme activity from the gene on the plasmid.

A RSF1010-trp hybrid plasmid which contained the tryptophan operon of Escherichia coli was introduced into Pseudomonas aeruginosa trp cells by transformation. From the Trp+ transformants several deletion plasmids were obtained, and their physical maps with restriction endonucleases were constructed. P. aeruginosa trp cells with these plasmids showed at first more than 100 times higher levels of tryptophan synthetase beta activity over that of the control P. aeruginosa wild-type cells, but these levels were drastically decreased by 1 week of successive transfers of cultures. This decrease in enzyme activity was found to be due to the change on the plasmids but not to the host cells. The production of E. coli tryptophan synthetase beta enzyme in P. aeruginosa cells was proved by immunological test.