Crystallization of restriction endonuclease BamHI with nonspecific DNA

Restriction endonucleases show extraordinary specificity in distinguishing specific from nonspecific DNA sequences. A single basepair change within th e recognition sequence results in over a millionfold loss in activity. To u nderstand the basis of this sequence discrimination, it is just as importan t to study the nonspecific complex as the specific complex. We describe her e the crystallization of restriction endonuclease BamHI with several nonspe cific oligonucleotides, The 11-mer, 5'-ATGAATCCATA-3', yielded cocrystals w ith BamHI, in the presence of low salt, that diffracted to 1.9 Angstrom wit h synchrotron radiation. The cocrystals belong to the space group P2(1)2(1) 2(1) with unit cell. dimensions of a = 114.8 Angstrom, b = 91.1 Angstrom, c = 66.4 Angstrom, alpha = 90 degrees, beta = 90 degrees, gamma = 90 degrees . This success in the cocrystallization of BamHI with a nonspecific DNA pro vides insights for future attempts at crystallization of other nonspecific DNA protein complexes. (C) 2000 Academic Press.