Bacterial Strain JM109 is a useful host for transformation of pGEM® Vectors and for production of single-stranded DNA from M13 or phagemid vectors. The strain grows well and is transformed efficiently by a variety of methods. Because JM109 is recA– and lacks the E. coli K restriction system, there is no undesirable restriction of cloned DNA or recombination with host chromosomal DNA. The endonuclease A– mutation leads to an improved yield and quality of isolated plasmid DNA.
JM109 is deficient in β-galactosidase activity due to deletions in both genomic and episomal copies of the lacZ gene. The deletion in the episomal (F´ factor) copy of the lacZ gene (lacZΔM15) can be complemented by addition of a functional α-peptide encoded by a pGEM®-Z or pGEM®-Zf Vector. If complementation does not occur, bacterial colonies are white. To maintain the F´, JM109 should be grown on minimal (M-9) media supplemented with 1mM thiamine.
Genotype: endA1, recA1, gyrA96, thi, hsdR17 (rk–, mk+), relA1, supE44, Δ( lac-proAB), [F´ traD36, proAB, laqIqZΔM15].