Plasmids

Plasmids - circular dsDNA, autonomously replicating, require host for replication machinery, energy, etc., can't leave the cell so don't kill the cell, used as cloning vectors

First plasmid discovered in Shigella strains in Japan that caused dysentary and were resistant to sulfonamides; resistance was conferred by a plasmid

Plasmids carry antibiotic resistance genes, virulence genes, colicin genes, heavy metal resistance genes

Replicate by:

1) Bidirectional (or unidirectional) replication (when replicate along with the host chromosome)

2) Rolling circle replication (when replicate independent of host chromosome)

F plasmid has 2 origins of replication, one for bidirectional (for use when cell divides) and one for rolling circle (for use when plasmid is transferred during conjugation)

Lysogeny (In "higher" organisms, it's called latency not lysogeny)

Virus can either exist as a plasmid (e.g. P1) or as part of the host chromosome (e.g. lambda)

Host is called a lysogen. Integrated virus is called a provirus

Replicon - any molecule of nucleic acid that has an ori so it controls its own replication

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Last updated: 9-April-98 / laa