Bacteriophage lambda int protein recognizes two classes of sequence in the phage att site: characterization of arm-type sites.

Purified int protein from bacteriophage lambda binds to specific sites in DNA that are not part of the functional attachment sites (non-att DNA) as well as to specific sites in att DNA. Analysis of non-att sites protected from nucleases by int has permitted definition of two distinctly different consensus recognition sequences, one of which, the arm-type sequence, is characterized in this report. Both types of recognition sequence occur in attP; five copies of the arm-type consensus sequence are located distant from the crossover region in the P1, P2, and P' arm protected regions. The second type of recognition sequence occurs at the crossover region. Modification of int with N-ethylmaleimide selectively alters its interaction with arm-type sequences.