Localization of a genetic region involved in McrB restriction by Escherichia coli K-12.

A 5,500-base-pair BglII-EcoRI fragment proximal to the hsd genes of Escherichia coli K-12 has been cloned in the plasmid vector pUC9. The resultant hybrid plasmid was shown to complement the mcrB mutation of E. coli K802. The presence of the hybrid plasmid in strain K802 caused an 18.3-fold drop in transformation efficiency with AluI-methylated pACYC184 relative to unmethylated pACYC184. These results indicate that the cloned DNA is involved in the McrB system restriction of 5-methylcytosine DNA.