Drybench Plasmid.
Selection markers beyond ampicillin
A selection marker is a gene that lets only cells carrying the plasmid grow; many plasmids carry one, and some carry two.
Two markers on pBR322
pBR322 was built to carry resistance to both ampicillin and tetracycline (Bolivar et al. 1977). Cloning into a site inside one of the two genes disrupts that resistance while keeping the other, so recombinant plasmids can be found by testing colonies on each antibiotic (insertional inactivation).
The tetracycline resistance gene, tet, encodes a membrane protein; its sequence is part of pBR322's complete sequence (Sutcliffe 1979).
Markers in other vectors
Vectors for other hosts carry other markers, such as the neomycin phosphotransferase gene for kanamycin or G418, chloramphenicol acetyltransferase for chloramphenicol, and hygromycin, puromycin and blasticidin resistance genes for mammalian cells. The annotation library holds several of these, each from its own public record.
See it on a real plasmid
Open pBR322 and find TetR and AmpR, and the unique cutters inside each.
A resistance protein is a finished protein at work, as the tour's last stop shows for haemoglobin.
References
- Bolivar F, Rodriguez RL, Greene PJ, et al. Construction and characterization of new cloning vehicles. II. A multipurpose cloning system. Gene 1977;2:95-113. PubMed 344137
- Sutcliffe JG. Complete nucleotide sequence of the Escherichia coli plasmid pBR322. Cold Spring Harb Symp Quant Biol 1979;43:77-90. PubMed 383387
Statements summarised by the site's builder from the references, for scientific review.