Non-random distribution of transduction termini in transductants from the integrated R plasmid, R100-1.

Tra+ and tra- derivatives of drug resistance plasmid, R100-1, were isolated by phage P1 from an Hfr donor with integrated R100-1 and then analyzed by complementation tests with tra- point mutants of Flac. Tra+ derivatives of R100-1 carrying tetracycline resistance alone and those carrying all six drug-resistrance genes could support transfer of tra- point mutants of Flac except Flac traJ, whereas all of tra- derivatives of R100-1 failed to complement any one of tra- point mutants of Flac. This suggests that these tra- derivatives of R100-1 carrying tetracycline resistance gene are deleted for all the transfer genes impaired in the Flac point mutants tested. We assume a "hot point", probably a specific base sequence similar to an IS element, at the left of the tetracycline gene (Fig. 1) becomes a transduction terminus in transduction of the integrated R100-1 by phage P1. Complementation analysis of tra- derivatives carrying five resistance genes except the tetracycline gene led us to a supposition that a gene(s), probably analogous to traJ of the F plasmid, is located on R100-1 near the tetracycline gene which plays an important regulatory role for self-transfer as well as for the complementation of tra- Flac mutants.