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Plasmids containing repetitive DNA sequences, such as those derived from retroviruses and lentiviruses, are susceptible to loss of integrity due to recombination events. In addition, GC- or AT- rich sequences (>70%) and sequences prone to the formation of secondary structures are notoriously difficult to clone. When cloning unstable DNA, choose a competent cell strain designed for the task. Bacteria with defective recombinases are more likely to faithfully replicate plasmids bearing unstable DNA inserts.

Use Stbl competent cells to avoid DNA recombination while cloning

Stbl competent cells express mutated forms of the RecA protein, rendering them recombination defective. Additional variations in genotype contribute to the ability of these strains to maintain plasmid integrity during cloning and replication. Notably, the Stbl3 strain demonstrated an exceptional maintenance of stability of an instability-prone lentiviral vector plasmid [1] and is the strain used in the seminal CRISPR-Cas9 protocol [2].

Learn more about propagating unstable DNA constructs

Compare Stbl competent cells for cloning unstable DNA

Three strains of Invitrogen Stbl competent cells are available, and each has properties that impact its performance with plasmids of various size and origin.

ProductStbl2 competent cell kit box, 5 blue-capped tubes, 2 vials of growth media, and 1 tube of control DNAMultiShot Stbl3 competent cell kit box, 1 foil-sealed plate, 2 vials of growth media, and 1 tube of control DNAStbl4 competent cell kit box, 5 cell tubes, 2 vials of growth media, and 1 tube of control DNA
MAX Efficiency Stbl2 Chemically Competent CellsStbl3 Chemically Competent 
E. coli
ElectroMAX Stbl4 Competent Cells
Recommended forCloning direct repeat retroviral sequences and tandem array genesCloning direct repeats found in lentiviral expression vectorsGenerating complex cDNA and genomic libraries
Derived from strainE. coli JM109/J5E. coli HB101Stbl2/E. coli JM109/J5
Transformation efficiency>1 x 109 cfu/µg>1 x 10cfu/µg>5 x 109 cfu/µg
Type of transformationChemical/Heat shockChemical/Heat shockElectroporation
Compatible plasmid size>20 kb>20 kb>100 kb
Blue/white screening 
Contains F´ episome for making single-stranded DNA 
Available format(s)
Still not sure which Stbl competent cells are right for your experiment?

Competent cells: Featured products

In addition to competent cells, we offer a broad suite of products for the cloning workflow.


Have any questions on competent cells or transformation? Click on the resources listed below to access overviews, videos, genotype guides, and educational resources.

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