XbaI is blocked by overlapping dam methylation. If the XbaI recognition site is preceded by GA or followed by TC, the Dam methylase within most E. coli cloning strains will methylate the GATC site. For example, XbaI sites gaTˆCTAGA and TˆCTAGAtc will be blocked by methylation. To avoid dam methylation use a dam-deficient strain such as dam-/dcm- Competent E. coli (#C2925). For up-to-date information about methylation sensitivities, please visit Dam-Dcm and CpG Methylation or REBASE.