Most strains used by molecular biologists are derivatives of E. coli K-12, and possess both Dam and Dcm, but there are commercially available strains that are dam-/dcm- (lack of activity of either methylase).
A maioría das cepas utilizadas polos biólogos moleculares son derivadas de E. coli K-12, e posúen tanto metilases Dam coma Dcm, pero disponse comercialmente de cepas que son dam-/dcm- (carecen da actividade de ambas as metilases).