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wild-type quiescent flagella tothatinactively beatingflagella using Here wecomparedcentral pairconformationinstraight, forces forcentral pairrotationandtwistareunknown. correlates withatwistedcentral pairstructure,propulsive bend propagationinflagella ofmany organismsandrotation David R.Mitchell andMasako Nakatsugawa chemotaxis andmucociliaryclearanceinmetazoansfor- essential forawiderangeofbiologicalprocessessuchassperm of ciliaryandflagellarmotility. and supportaspecificmodelofcentralpair-basedregulation others (Omotoetal.,1999).Ourresultsexplainthisdichotomy tral pairinciliaandflagellaofsomeorganismsbutnot This taskiscomplicatedbytheapparentrotationofcen- pattern ofdyneinactivationnecessaryforbendpropagation. relationship betweentheseasymmetricstructuresandthe central paircomplexes,itisessentialtofirstunderstandthe elusive. Tobetterunderstandtheconservedfunctionof 1979), buttheprecisefunctionofthesestructuresremains radial spokesaremissing(Witmanetal.,1978;Baccetti Flagella becomeparalyzedwheneitherthecentralpairor evolution intotoday’sphylogeneticallydiverseorganisms. this machineryhassurvivedwithlittlemodificationduring very earlyasanessentialelementinflagellarmotility,and Therefore, thecentralpairmicrotubulecomplexevolved 9 eukaryotes musthavebeenasingle-celledorganismwith in Bend propagation drives central pairrotation lack radial spoke heads. Twists occurinquiescentflagella tain organismswith9 Because allmajorphylogeneticdivisionsofeukaryotescon- ofCellandDevelopmentalDepartment Biology, State University ofNew York Upstate Medical University, Syracuse, NY13210 Introduction © Key words: cilia;radial spoke;dynein;motility;microtubule (315) 464-8535.email:[email protected] sity, 750E.AdamsSt.,Syracuse,NY 13210.Tel.:(315)464-8575.Fax: mental Biology,StateUniversityof NewYorkUpstateMedicalUniver- Address correspondencetoD.R.Mitchell, Dept.ofCellandDevelop- http://www.jcb.org/cgi/doi/10.1083/jcb.200406148 The Journal ofCellBiology