The amino terminal domain of bacteriophage lambda integrasefolds into a three-stranded, antiparallel beta-sheet that packsagainst a C-terminal alpha-helix, adopting a fold that isstructurally related to the three-stranded beta-sheet family ofDNA-binding domains (which includes the GCC-box DNA-bindingdomain and the N-terminal domain of Tn916 integrase). Thisdomain is responsible for high-affinity binding to each of thefive DNA arm-type sites and is also a context-sensitivemodulator of DNA cleavage [1]. Bacteriophage lambda integrase, N-terminal domain Phage_integ_N