The Muir lab is using novel techniques to study molecular recognition in prokaryotic and eukaryotic signal transduction. One of these techniques is a general approach to investigating protein activity called expressed protein ligation, which allows synthetic peptides and recombinant proteins to be chemoselectively linked together. Dr. Muir is currently using expressed protein ligation to study how histone modifications control the local structure and activity of chromatin and potassium channel selectivity. The lab has developed two ways to study protein function in vivo - both of which exploit protein splicing, in which an intervening sequence - termed an intein - catalyzes its removal from a host protein, the extein. In transsplicing, the intein is split into two pieces and splicing occurs only upon reconstitution of these fragments. The first of the techniques is a system that allows protein transsplicing to occur only in the presence of a small cell-permeable molecule. The second technique is for protein semisynthesis inside living cells. Another area of research in the Muir lab focuses on quorum sensing in Staphylococcus aureus. Dr. Muir is studying a class of the bacterium's secreted peptides that has the ability to activate or inhibit expression of virulence, depending on which strain of S. aureus the peptides encounter.