High-resolution atomic force microscopy of duplex and triplex DNA molecules

摘要

Double-stranded poly(dG) - poly(dC) and triple-stranded poly( dG) - poly( dG) - poly( dC) DNA were deposited on the modified surface of highly oriented pyrolitic graphite ( HOPG) and visualized using atomic force microscopy with high-resolution ( radius of similar to 1 nm) tips. The high resolution attained by this technique enabled us to detect single-stranded regions in double-stranded poly( dG) - poly( dC) and double-stranded and single-stranded regions in poly( dG) - poly( dG) - poly( dC) triplexes, as well as to resolve the helical pitch of the triplex molecules. We could also follow the reaction of G-strand extension in poly( dG) - poly( dC) by the Klenow exo(-) fragment of DNA polymerase I. This approach to molecular visualization could serve as a useful tool for the investigation of irregular structures in canonical DNA and other biopolymers, as well as studies of the molecular mechanisms of DNA replication and transcription.