Derepression of E. coli trp operon on interfamilial transfer

Abstract

THE P-group R factor RP4 originally isolated from Pseudomonas aeruginosa can be transferred to many Gram-negative bacteria^1–3. In spite of its large molecular weight, RP4 has only one site susceptible to each of EcoRI (ref. 4), HindIII (ref. 5) and BamNI (data not shown) restriction endonucleases. We have constructed an RP4-trp plasmid consisting of RP4 DNA and the complete tryptophan operon of E. coli obtained from bacteriophage λtrpE-A_60-3 in vitro⁶. We reported that the tryptophan synthetase activity in the strain carrying RP4-trp plasmid was repressed by exogenous tryptophan⁷. Manson and Yanofsky have reported that the E. coli trp operon on the colVB plasmid was similarly regulated in other enteric species⁸. We show here that the RP4-trip plasmid in E. coli can be transferred by conjugation to Pseudomonas aeruginosa which belongs to a different family from E. coli, converting Pseudomonas Trp⁻ phenotype to Trp⁺. The levels of tryptophan-synthesising enzymes in P. aeruginosa carrying RP4-trp plasmid are much higher than those in the wild strain, and they are not controlled by the repression system in P. aeruginosa cells.