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 [1].

1: Arm-site binding by lambda -integrase: solution structure and functional characterization of its amino-terminal domain. Wojciak JM, Sarkar D, Landy A, Clubb RT; Proc Natl Acad Sci U S A. 2002;99:3434-3439. PMID:11904406