Interaction of T4 phage DNA-[N6-adenine]-methyltransferase with substrates containing defective recognition sites

The effect of the structure of recognition site GATC in a substrate duplex on its complexation with DNA-[N6-adenine]-methyltransferase of T4 phage (T4 MTase) was studied. The pel retardation method was employed to reveal the complexes. As compared with the native duplexes, the majority of defective duplexes had the same or even better affinity to T4 MTase; however, no correlation was found between the complex stability and effectiveness of the duplexes as substrates for methylation. Apparently, formation of a stable enzyme-DNA complex does not require continuity of the two strands of the duplex and perfect base pairing in the recognition site. A half of the constituents of the recognition site suffices for stable complexes with T4 MTase to form. Deoxyguanosine residues in both strands of the modified GATC are shown to be indispensable for complex formation.