Editing Cloning vector (section)

===Selectable marker===
A [[selectable marker]] is carried by the vector to allow the selection of positively [[Transformation (genetics)|transformed]] cells.  [[Antibiotic]] resistance is often used as marker, an example being the [[beta-lactamase]] gene, which confers resistance to  the [[penicillin]] group of [[beta-lactam antibiotics]] like [[ampicillin]].  Some vectors contain two selectable markers, for example the plasmid pACYC177 has both ampicillin and [[kanamycin]] resistance gene.<ref name = "Casali_2003">{{cite book | vauthors = Casali N, Preston A  |title= ''E. coli'' plasmid vectors |series=Methods in Molecular Biology |volume=235 |page=23 |url=https://books.google.com/books?id=r6QC0hTwsrwC&pg=PA23 |isbn=978-1-58829-151-6 |year=2003 }}</ref> Shuttle vector which is designed to be maintained in two different organisms may also require two selectable markers, although some selectable markers such as resistance to [[zeocin]] and [[hygromycin B]] are effective in different cell types.  [[Auxotrophic]] selection markers that allow an auxotrophic organism to grow in [[minimal growth medium]] may also be used; examples of these are ''[[Leucine|LEU2]]'' and ''[[URA3]]'' which are used with their corresponding auxotrophic strains of yeast.<ref>{{cite journal | vauthors = Romanos MA, Scorer CA, Clare JJ | title = Foreign gene expression in yeast: a review | journal = Yeast | volume = 8 | issue = 6 | pages = 423–488 | date = June 1992 | pmid = 1502852 | doi = 10.1002/yea.320080602 | s2cid = 15674832 }}</ref>

Another kind of selectable marker allows for the positive selection of plasmid with cloned gene.  This may involve the use of a gene lethal to the host cells, such as [[barnase]],<ref>{{cite journal | vauthors = Yazynin SA, Deyev SM, Jucovic M, Hartley RW | title = A plasmid vector with positive selection and directional cloning based on a conditionally lethal gene | journal = Gene | volume = 169 | issue = 1 | pages = 131–132 | date = February 1996 | pmid = 8635737 | doi = 10.1016/0378-1119(95)00814-4 | url = https://zenodo.org/record/1258531 }}</ref> [[CcdA/CcdB Type II Toxin-antitoxin system|Ccda]],<ref>{{cite journal | vauthors = Bernard P | title = Positive selection of recombinant DNA by CcdB | journal = BioTechniques | volume = 21 | issue = 2 | pages = 320–323 | date = August 1996 | pmid = 8862819 | doi = 10.2144/96212pf01 | doi-access = free }}</ref> and the [[ParDE type II toxin-antitoxin system|parD/parE]] toxins.<ref>{{cite journal | vauthors = Gabant P, Van Reeth T, Drèze PL, Faelen M, Szpirer C, Szpirer J | title = New positive selection system based on the parD (kis/kid) system of the R1 plasmid | journal = BioTechniques | volume = 28 | issue = 4 | pages = 784–788 | date = April 2000 | pmid = 10769758 }}</ref><ref>{{cite journal | vauthors = Kim HG, Kim HS, Hwang HJ, Chung SK, Lee JM, Chung DK | title = Construction of a pTOC-T vector using GST-ParE toxin for direct cloning and selection of PCR products | journal = Biotechnology Letters | volume = 26 | issue = 21 | pages = 1659–1663 | date = November 2004 | pmid = 15604816 | doi = 10.1007/s10529-004-3518-z | s2cid = 10312859 }}</ref>  This typically works by disrupting or removing the lethal gene during the cloning process, and unsuccessful clones where the lethal gene still remains intact would kill the host cells, therefore only successful clones are selected.