plasmid:   an extrachromosomal genetic element that occurs in many bacterial strains. Plasmids are circular deoxyribonucleic acid (DNA) molecules that replicate independently of the bacterial chromosome;  may confer a selective advantage. Colicinogenic (or Col ) factors, determines the production of proteins called colicins, which have antibiotic activity and can kill other bacteria. R factors, confer resistance to ntibiotics. Some Col factors and R factors can transfer themselves from one cell to another and thus are capable of spreading rapidly through a bacterial population.  

Plasmids are extremely valuable tools in the fields of molecular biology and genetics, gene cloning, recombinant protein production, and gene therapy research. Aplasmid is cut at a specific sites  using enzymes called restriction endonucleases, other DNA elements are spliced into the plasmid. The result - a recombinant DNA molecule, is then introduced into bacterial cells.  (adapted from the Britannica)

Find out more in:

The Biology of Plasmids 

David K. Summers / Paperback / Published 1996

Plasmids : A Practical Approach (The Practical Approach, No 138)

K.G. Hardy(Editor) / Hardcover / Published 1994

 

The Yeast Two-Hybrid System (Advances in Molecular Biology) 

Paul L. Bartel(Editor), Stanley Fields (Editor) / Paperback / Published 1997

Bacterial Conjugation

Don B. Clewell(Editor) / Hardcover / Published 1993

Pathogenicity Islands and Other Mobile Virulence Elements

James B. Kaper(Editor), Jorg Hacker (Editor) / Hardcover / Published 1999

Extrachromosomal Elements in Lower Eukaryotes (Basic Life Sciences, Vol 40)

Reed B. Wickner(Editor) / Hardcover / Published 1987

The Hyman method : oligonucleotide synthesis and plasmid preparation

Edward David Hyman / Published 1995

Molecular Biology, Pathogenicity, and Ecology of Bacterial Plasmids

S Levy / Hardcover / Published 1981

Molecular Genetics of Escherichia Coli (Guilford Molecular Cell Biology Series)

Peter Smith-Keary / Paperback / Published 1989

Molecular Genetics of Escherichia Coli (Guilford Molecular Cell Biology Series)

P.F Smith-Kerry / Hardcover / Published 1989

 

Plasmids : A Practical Approach (The Practical Approach, No 138)

K.G Hardy(Editor) / Paperback / Published 1994