<p>The amino terminal domain of bacteriophage lambda integrase folds into a three-stranded, antiparallel beta-sheet that packs against a C-terminal alpha-helix, adopting a fold that is structurally related to the three-stranded beta-sheet family of DNA-binding domains (which includes the GCC-box DNA-binding domain and the N-terminal domain of Tn916 integrase). This domain is responsible for high-affinity binding to each of the five DNA arm-type sites and is also a context-sensitive modulator of DNA cleavage [<cite idref="PUB00028838"/>]. </p>