TnA-directed deletion of the trp operon from RSF2124-trp in Escherichia coli.

Plasmid pMT-trp was constructed by digestion of RSF2124-trp with restriction endonuclease PstI and ligation with T4 ligase. In pMT-trp about 78% of the DNA of transposon TnA from RSF2124-trp was deleted, and hence the gene for ampicillin resistance was lost. All Trp- segregants from pMT-trp carriers in Escherichia coli W3110 and its derivatives were found to have lost the entire plasmid. On the other hand, deletion plasmids which had lost the trp operon were found among Trp- segregants from RSF2124-trp carriers, particularly from the mutant strain trpAE1 trpR tnaA. The experimental fact that deletion occurred exclusively in RSF2124-trp suggests that the presence of TnA in the plasmid (RSF2124-trp) was responsible for the deletion.