The archaeal flagellum: a different kind of prokaryotic motility structure

The archaeal flagellum is a unique motility apparatus distinct in compositi on and likely in assembly from the bacterial flagellum. Gene families compr ised of multiple flagellin genes co-transcribed with a number of conserved, archaeal-specific accessory genes have been identified in several archaea. However, no homologues of any bacterial genes involved in flagella structu re have yet been identified in any archaeon, including those archaea in whi ch the complete genome sequence has been published. Archaeal flagellins pos sess a highly conserved hydrophobic N-terminal sequence that is similar to that of type IV pilins and clearly unlike that of bacterial flagellins. Als o unlike bacterial flagellins but similar to type IV pilins, archaeal flage llins are initially synthesized with a short leader peptide that is cleaved by a membrane-located peptidase. With recent advances in genetic transfer systems in archaea, knockouts have been reported in several genes involved in flagellation in different archaea. In addition, techniques to isolate fl agella with attached hook and anchoring structures have been developed. Ana lysis of these preparations is under way to identify minor structural compo nents of archaeal flagella. This and the continued isolation and characteri zation of flagella mutants should lead to significant advances in bur knowl edge of the composition and assembly of archaeal flagella. (C) 2001 Federat ion of European Microbiological Societies. Published by Elsevier Science B. V. All rights reserved.