The Function and Organization of Plasmids
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In 1952, Joshua Lederberg coined the term plasmid to describe any bacterial genetic element that exists in an extrachromosomal state for at least part of its replication cycle (1 ). As this description included bacterial viruses, the definition of what constitutes a plasmid was subsequently refined to describe exclusively or predominantly extrachromosomal genetic elements that replicate autonomously. Plasmids are now known to be present in most species of Eubacteria that have been examined, as well as in Archaea and lower Eukarya (2 ).
