IncP plasmids are unusually effective in mediating conjugation of Escherichia coli and Saccharomyces cerevisiae: Involvement of the Tra2 mating system

Mobilizable shuttle plasmids containing the origin-of-transfer (oriT) regio n of plasmids F (IncFI), ColIb-P9 (IncI1), and RP4/RP1 (IncP alpha) were co nstructed to test the ability of the cognate conjugation system to mediate gene transfer from Escherichia coli to Saccharomyces cerevisiae. Only the P alpha system caused detectable mobilization to yeast, giving peak values o f 5 x 10(-5) transconjugants per recipient cell in 30 min. Transfer of the shuttle plasmid required carriage of oriT in cis and the provision in trans of the P alpha Tra1 core and Tra2 core regions. Genes outside the Tra1 cor e did not increase the mobilization efficiency. All 10 Tra2 core genes (trb B, -C, -D, -E, -F, -G, -H, -I, -J, and -L) required for plasmid transfer to E. coli K-12 were needed for transfer to yeast. To assess whether the mati ng-pair formation (Mpf) system or DNA-processing apparatus of the P alpha c onjugation system is critical in transkingdom transfer, an assay using an I ncQ-based shuttle plasmid specifying its own DNA-processing system nas devi sed. RP1 but not ColIb mobilized the construct to yeast, indicating that th e Mpf complex determined by the Tra2 core genes plus traF is primarily resp onsible for the remarkable fertility of the P alpha system in mediating gen e transfer from bacteria to eukaryotes.