Triparental crosses in Streptomyces coelicolor A3(2) as a means of demonstrating the de-repression of SCP1 plasmid conjugative functions.

A conjugative plasmid free in the cytoplasm promotes recombination if it is transferred to two plasmid-less strain in triparental crosses of Streptomyces coelicolor. The recombination frequency is the same as that of biparental crosses between a plasmid-bearing and a plasmid-less strain. The "conjugative" functions of the plasmid are responsible for recombinant formation. Hyphal contact and subsequent heterokaryon formation are necessary but not sufficient steps for the recombinant process. This paper shows that the presence of a conjugative plasmid is necessary for chromosome mobilization and subsequent recombinant formation.