Abstract
Argonaute (Ago) proteins are key players in gene regulation in eukaryotes and host defense in prokaryotes. For specific interference, Ago relies on base pairing between small nucleic acid guides and complementary target sequences. To efficiently scan nucleic acid chains for potential targets, Ago must bypass both secondary structures in mRNA and single stranded DNA as well as protein barriers. Through single-molecule FRET, we reveal that lateral diffusion is mediated mainly through protein-nucleic acid interactions, rather than interactions between the guide and targeted strand. This allows Ago to scan for targets with high efficiency but without maintaining tight contact with the DNA backbone. Real-time observations show that Ago glides short distances over secondary structures while using intersegmental jumps to reduce scanning redundancy and bypass protein barriers. Our single-molecule method in combination with kinetic analysis may serve as a novel platform to study the effect of sequence on search kinetics for other nucleic acid-guided proteins.
