SUMMARY: Recombinant plasmids between RI and P- and between Rb and were produced by phage PL transductions of the respective R factors to Providence P29 strains harbouring P- The P-R (the superior line indicating the transduced R factor) recombinant plasmid transfers and all determinants of the R factor to strains and at high frequencies which approach inter-Proteus transfer of the parental plasmids. The -Rb recombinant transfers and only marker K of the parent R factor, at frequencies of P- inter-Proteus transfer. Both recombinants possess the compatibility property and possibly most other features of P- Transductions of the P-R recombinant with phages PL and 34 differ. Those with the former vector to P29 yield transductants which have markers ACKSu but not or S and do not transmit markers conjugally. Conjugal transferability is restored with transductions of the recombinant to P29 carrying a resident P-; these transductants then transmit R with phage 34 to strains of produce transductants which possess all the resistance determinants and which transfer these conjugally, but in which does not appear. A spontaneous segregant of the P-R recombinant retained the high transfer rate and other properties of the parent. Transduction of this segregant to strains of P29 and resulted in transductants which carried markers ACKSu and ACKSSu respectively but could not transfer them by conjugation. Transductions of the segregant to strains harbouring P- again produced recombinant plasmids at low rates which transmitted the above groups of resistance determinants and at frequencies similar to those of the original recombinant. Transductions of the P-Rb recombinant with either phage yielded transductants carrying K (and able to transmit it conjugally) but never any carrying


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