E.coli Strain Genotypes

a The original E. coli K-12 strain was an F + λ lysogen, but most K-12 derivatives in common use have been cured of the F factor and prophage and these are indicated only when present. All other genes in these strains are presumed to be wild-type except for the genotype markers noted in the second column.

b AS1 is also known as MM294cI +, BNN102 is also known as C600 hflA.

c Both CJ236 and BW313 are commonly used in oligonucleotide-directed mutagenesis, pCJ105, the plasmid CJ236 carries, is not relevant for this application.

d Three strains are in circulation. DH5 is a derivative of DH1 that transforms at higher efficiency. DH5α and DH5αF’ are derivatives that carry a deletion of the lac operon and φ80 prophage that directs synthesis of the omega fragment of β-galactosidase. DH5αF’ carries an F’ factor as well. DH5α and DH5αF’ are proprietary strains and the cells are prepared in some way that allows them to be transformed with slightly higher efficiency than DH5.

e In this strain, the area of the chromosome that contains the hsd genes was derived from the related B-strain of E. coli.

f The continued presence of the F’ factor in JM strains can be insured by starting cultures only from single colonies grown on minimal plates that do not contain proline. These strains encode the omega fragment of lacZ and are frequently used with vectors that direct the synthesis of the lacZ alpha fragment. These strains are frequently used with M13 vectors for DNA sequencing.

g It is not known whether this strain has markers other than those listed.
h pMC9, the plasmid in the Y strains listed here, directs the synthesis of large amounts of lac repressor It also confers resistance to tetracycline and ampicillin (Miller et al., 1984, EMBO.J.3:3117-3121).

Adapted from Current Protocols in Molecular Biology, Ausubel, Brent, Kingston, Moore, Seidman, Smith, and Struhl eds.