Bacterial plasmids: their extraordinary contribution to molecular genetics.

Reviewed here are certain of the extraordinary contributions to molecular genetics that have resulted from the study of bacterial plasmids. Work with plasmids has led to both the 'operon' and 'replicon' concepts, and has provided seminal information about bacterial conjugation and fertility, recombination, transposable genetic elements, genome evolution and antisense RNA. Studies of plasmid functions have yielded important findings about the regulation of DNA replication, DNA topology and partitioning, gene control signals and restriction/modification enzymes. Plasmids have had a central role in the development of DNA cloning (recombinant DNA) methods; additionally, they have provided a paradigm for both the co-transformation of non-selected DNA into eukaryotic cells and the creation of the artificial chromosomes.