Three-arm nucleic acid junctions are flexible.

Nucleic acid junctions are stable analogs of branched DNA structures which occur transiently in living systems. We show here that junctions which contain three double helical arms can be enzymatically oligomerized, using conventional sticky-ended ligation procedures, to create larger complexes. The products consist of a series of linked junctions separated by 20 base pairs. Junction dimers are formed that have free termini only, whereas trimers and larger species are found to be both unclosed and cyclized. The formation of a series of macrocyclic products which, surprisingly, begins with trimers and tetramers indicates that this junction is flexible about a bending axis, and perhaps twist-wise as well. We have obtained the same results from three different 3-arm junctions, two in which the junction is flanked by a 3 Watson-Crick base pairs, and one in which a G-G base pair flanks the junction.