title: Building a flagellum in biological outer space.
abstract: Flagella, the rotary propellers on the surface of bacteria, present a paradigm for how cells build and operate complex molecular 'nanomachines'. Flagella grow at a constant rate to extend several times the length of the cell, and this is achieved by thousands of secreted structural subunits transiting through a central channel in the lengthening flagellum to incorporate into the nascent structure at the distant extending tip. A great mystery has been how flagella can assemble far outside the cell where there is no conventional energy supply to fuel their growth. Recent work published by Evans et al. [Nature(2013) 504: 287-290], has gone some way towards solving this puzzle, presenting a simple and elegant transit mechanism in which growth is powered by the subunits them selves as they link head-to-tail in a chain that is pulled through the length of the growing structure to the tip. This new mechanism answers an old question and may have resonance in other assembly processes.
authors.affiliation: Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, United Kingdom.
authors.forename: Lewis D B
authors.initials: LD
authors.lastname: Evans
authors.affiliation: Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, United Kingdom.
authors.forename: Colin
authors.initials: C
authors.lastname: Hughes
authors.affiliation: Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, United Kingdom.
authors.forename: Gillian M
authors.initials: GM
authors.lastname: Fraser
keywords: Type III export; bacterial flagella; cell motility; chain mechanism; rotary nanomachine