The specificity (S) subunit of the restriction enzyme EcoKI imparts specificity for the sequence AAC(N6)GTGC. Substitution of thymine with bromodeoxyuridine in a 25 bp DNA duplex containing this sequence stimulated UV light-induced covalent crosslinking to the S subunit. Crosslinking occurred only at the residue complementary to the first adenine in the AAC sequence, demonstrating a close conta...
