PNA-dependent gene chemistry: stable coupling of peptides and oligonucleotides to plasmid DNA.

Two approaches are described for stably conjugating peptides, proteins and oligonucleotides onto plasmid DNA. Both methods use a peptide nucleic acid (PNA) clamp, which binds irreversibly and specifically to a binding site cloned into the plasmid. The first approach uses a biotin-conjugated PNA clamp that can be used to introduce functional biotin groups onto the plasmid to which streptavidin can bind. Atomic force microscopy images of linearized plasmid show streptavidin localized at the predicted PNA binding site on the DNA strand. Peptides and oligonucleotides containing free thiol groups were conjugated to maleimide streptavidin, and these streptavidin conjugates were bound to the biotin-PNA-labeled plasmid. In this way, peptides and oligonucleotides could be brought into stable association with the plasmid. A second approach used a maleimide-conjugated PNA clamp. Methods are described for conjugating thiolated peptides and oligonucleotides directly to the maleimide-PNA-DNA hybrid. This straightforward technology offers an easy approach to introduce functional groups onto plasmid DNA without disturbing its transcriptional activity.