Denaturation and Association of DNA Sequences by Certain Polypropylene Surfaces

We observed that DNA fragments in room temperature solution undergo low levels of denaturation in the presence of certain types of polypropylene tube surfaces. If the fragments contain (GT)n·(CA)nor (GA)n·(CT)nsequences, multimeric complexes are also formed. This surface activity is inhibited by addition of micromolar concentrations of an oligodeoxyribonucleotide of arbitrary sequence to the tube prior to adding the double-stranded DNA. The reaction was not observed in tubes made of borosilicate glass or in polypropylene-based tubes designed to have low-binding properties. In the case of the DNA fragments that form surfaced-induced multimers, similar complexes can be obtained by denaturation and renaturation of the fragment (“induced” association) without regard to the type of tube surface. However, induced association requires the presence of magnesium ions or polyethylene glycol (or concentration by evaporation) for efficient formation of complexes, whereas surface-dependent dissociation has no such requirements. This difference in buffer requirement suggests that association as well as denaturation takes place on the surface. We suggest models for the formation and structure of these complexes based on surface-dependent denaturation followed by misaligned renaturation of repeated sequences and intermolecular pairing of unpaired regions. This denaturation and complex formation may be important for the interpretation of protein–DNA binding experiments and might be related to hydrophobic interactions of DNAin vivo.