RETROTRANSFER OF INCP PLASMID R751 FROM ESCHERICHIA-COLI MAXICELLS - EVIDENCE FOR THE GENETIC SUFFICIENCY OF SELF-TRANSFERABLE PLASMIDS FORBACTERIAL CONJUGATION

Gene transfer between organisms is a prime contributor to evolution. B acterial conjugation is probably the most important mechanism by which genes are spread among prokaryotes and perhaps also contributes to eu karyotic evolution. Conjugation is mediated by plasmids. The mechanism of conjugation remains ill-understood despite progress in the identif ication, mapping and sequencing of genes required for plasmid transmis sion. All conjugation-specific genes (those required only for DNA tran sfer and establishment) identified to date map to plasmids. We found t hat IncP plasmids could enter and subsequently convert maxicells, whic h are trapped in a metabolic state that prevents de novo expression of chromosomal genes, into conjugative donors. This suggests that IncP p lasmids encode not only necessary functions but indeed all functions s pecific to DNA transmission. Thus, like viruses, plasmids can convert non-viable cells into gene vectors.