Product Class: Strain

E. coli K12 ER1821

Limit of 1 per order. Although this product is free of charge, freight charges will apply. For US customers, available via phone ordering only (1-800-632-5227). For international customers, please contact your local NEB subsidiary or distributor.
Catalog #SizeConcentration


MM294 background: McrA- McrBC- EcoK r- m- Mrr- . A suspension of E. coli ER1821 which has been grown in rich medium and brought to 50% glycerol.


F- glnV44 e14-(McrA-) rfbD1? relA1? endA1 spoT1? thi-1 Δ(mcrC-mrr)114::IS10

Supporting Documents

The following is a list of Safety Data Sheet (SDS) that apply to this product to help you use it safely.


  1. Restriction Defects: McrA, McrBC, and Mrr all restrict methylcytosine-containing DNA methylated by the CpG methylase (M.Sss I) (1). In addition, McrA and McrBC specifically restrict DNA modified by different sets of more sequence-specific cytosine methylases (2).

    Mrr also restricts many methyladenine-containing sequences (3,4). Restriction by each of these three restriction systems individually (tested with λ DNA modified with the Sss I methylase and then packaged into phage) is: McrA, 250-fold; McrBC, 100-fold; Mrr, 200-fold. Cumulative restriction when all three are present in the same cell is 5,000-fold (1). In addition, EcoK restricts DNA not modified at K sites by 10-fold to 5,000-fold, depending on the number of sites (5). ER1821 lacks all four activities.


  1. Kelleher, J.E. and Raleigh, E.A. (1991). J. Bacteriol.. 173, 5220-5223.
  2. Raleigh, E.A. and Wilson, G. (1986). Proc. Natl. Acad. Sci. USA. 83, 9070-9074.
  3. Waite-Rees, P.A. et al. (1991). J. Bacteriol.. 173, 5207-5219.
  4. Heitman, J. and Model, P. (1987). J. Bacteriol.. 169, 3243-3250.
  5. Murray, N.E. et al. (1973). Mol. Gen. Genet.. 120, 261-281.