Abstract: The invention relates to a nucleic acid comprising at least one methylation-protectable restriction element, the methylation-protectable restriction element comprising: (i) a type IIS restriction enzyme recognition sequence, or a partial type IIS restriction enzyme recognition sequence, that is recognised by a type IIS restriction enzyme that cleaves outside of the recognition sequence; (ii) a DNA methylase recognition sequence that is recognised and methylated by a DNA methylase, wherein the DNA methylase recognition sequence is identical to, or is encompassed within, the type IIS restriction recognition sequence, such that methylation of the nucleic acid by the DNA methylase methylates the type IIS restriction enzyme recognition sequence and protects the nucleic acid from cleavage by the type IIS restriction enzyme; and (iii) a recognition sequence for a sequence-specific DNA-binding protein, wherein the recognition sequence is positioned such that the binding of the sequence-specific DNA-binding protein ov