EXTENSION OF DNA TRIPLE-HELIX FORMATION TO A NEIGHBORING (AT)(N) SITE

We have used DNase I footprinting to examine the formation of intermol ecular triple helices at a fragment containing the target sequence A(1 1)(AT)(6) .(AT)(6)T-11, using oligonucleotides designed to form parall el T . AT and G . TA triplets, We find that, although (TG), does not f orm a complex with (AT)(6) .(AT)(6), T-11(TG)(6) forms a stable struct ure producing a clear footprint which includes the (AT)(6) portion of the target site, This complex is not formed in the presence of magnesi um, but can be stabilised by either manganese or a tripler-binding lig and.,