Helicase is an important genome caretaker protein which plays a central role in biological processes including replication, transcription, recombination and repair of DNA. Helicase, by definition is an enzyme which unwinds a duplex nucleic acid into its single strand components. However, many helicases found in biological systems are not processive unwindases. We have employed single molecule fluorescence detection techniques to unveil detailed mechanism of noncanonical helicases which perform unique translocation activities.Using single molecule FRET, we discovered an unexpected shuttling motion of an e. coli protein, Rep. The ATP-driven repetitive translocation of Rep on single stranded DNA was visualized as a sawtooth pattern of FRET change. Furthermore, we showed that the repetitive motion may play a functional role of maintaining single strand DNA free of unwanted protein such as recombination protein, RecA (1).We have developed a newly developed single molecule fluorescence method, termed “protein induced fluorescence enhancement” (PIFE) to probe a translocation activity of an antiviral receptor protein, RIG-I. The translocation was inhibited by its own N-terminal CARD domain whereas the inhibition was completely lifted by a viral mimic RNA which contained unique pathogenic signatures. Our result demonstrates how RIG-I exhibits an exquisite mechanism to self-regulate its activity by sensing the pathogenic moiety (2).Reference1. S. Myong, I. Rasnik, C. Joo, T. M. Lohman, T. Ha, Nature 437, 1321 (Oct 27, 2005).2. S. Myong et al., Science 323, 1070 (Feb 20, 2009).