ECOS Blue (XL1-Blue)
XL1-Blue is the most popular strain for blue/white screening. It is also an excellent host strain for routine cloning application using plasmid or lambda vectors. XL1-Blue cells are endonuclease (endA) deficient, which greatly improve the quality of mini-prep DNA, and are recombination (recA) deficient, improving insert stability. The hsdR mutation prevents the cleavage of cloned DNA by the EcoK endonuclease system. The lacIqZ?M15 gene on the F´ episome allows blue-white color screening.