XL1 and XL2-Blue Competent Cells are versatile for routine cloning and allow blue-white colour screening for high efficiency cloning of methylated DNA.

• Designed to provide a host for optimal propagation of both plasmid and lambda phage vectors
• Available in a range of cloning efficiencies
• Available as economical subcloning-grade Competent Cells for routine procedures when DNA is not limited
• Available as supercompetent cells in a variety of strains at efficiencies greater than 1×10⁹ transformants/μg.
• Transformation efficiency for XL1-Blue MR and XL-1 Blue MRF’ supercompetent cells of ≥1×10⁹ transformants/μg
• Transformation efficiency for XL1-Blue MRF´ Kan supercompetent cells of ≥1×10⁹ transformants/μg
• Transformation efficiency for XL1-Blue MRF’ electroporation competent cells of ≥1×10¹⁰ transformants/µg
• Ultracompetent cells for the highest efficiency cloning of a variety of plasmids
• Deficient in all known E. coli K12 restriction systems to eliminate cleavage of eukaryotic DNA with methylation patterns that are different than the E. coli host methylation patterns
• Cloning methylated DNA is more efficient with restriction-minus competent cells

XL-1 Blue Competent Cells for routine cloning allow blue-white color screening, single-strand rescue of phagemid DNA, and preparation of high-quality plasmid DNA. Derivatives enable higher transformation efficiency, transformation of methylated DNA, choice of antibiotic resistance, and no F´ episome.For the greatest number of colonies, use electroporation-competent XL1-Blue cells or the high-efficiency derivative, XL2-Blue ultracompetent cells. When ultimate efficiency is not as critical, try the supercompetent-grade, competent-grade, or the subcloning grade competent cells.

XL-1 Blue MRF’ and XL-1 Blue MR competent cells allow high efficiency and representational cloning of methylated DNA. All known E. coli K12 restriction systems have been deleted. Use XL1-Blue MRF’ cells when cloning methylated cDNA or genomic DNA, or when cloning methylated PCR products.When the F’ episome and blue-white screening are unnecessary, use XL1-Blue MR supercompetent cells. When cloning tetracycline-resistant plasmids, use XL1-Blue MRF’ Kan supercompetent cells to select for the F’ episome and provide a more intense blue color for blue-white screening.

XL2-Blue - When DNA is methylated in a fashion unlike the bacterial host patterns, it is cleaved by the E. coli host restriction systems. Cleavage of DNA before host replication creates libraries that lack complete representation. Our MR (Minus Restriction) series of competent cells are deficient in all known E. coli K12 restriction systems and make it possible to clone methylated DNA, which can be very useful in epigenetic studies where DNA methylation, instead of changes in DNA sequence, may be associated with heritable changes in gene expression or cellular phenotype.

XL2-Blue MRF´ ultracompetent cells are high-efficiency derivatives of our XL1-Blue MRF´ supercompetent cells. Using ultracompetent cell technology, we have achieved transformation efficiencies of greater than 5×10⁹ transformants/µg of pUC18 DNA, making these ultracompetent cells an ideal choice for high-efficiency cloning. The XL2-Blue MRF´ (Minus Restriction) strain is deficient in all known restriction systems (McrA–, McrCB–, McrF–, Mrr–, HsdR–), preventing cleavage of cloned DNA that carries cytosine and/or adenine methylation, which is often present in eukaryotic DNA and cDNA. XL2-Blue MRF´ cells are restriction minus. The strain is endonuclease deficient (endA), greatly improving the quality of miniprep DNA, and recombination deficient (recA), helping to ensure insert stability. These cells allow blue-white screening for recombinant plasmids.