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1、J.gen.Virol.(1982),63,241-245.PrintedinGreatBritain241Keywords:coronavirus/freeze-drying/ultrastructureBovineEntericCoronavirusStructureasStudiedbyaFreeze-dryingTechnique(Accepted21June1982)SUMMARYAstrainofbovinecoronavirus(F15)wasstudiedbyelectronmicroscopyusingafreeze-
2、dryingtechnique.Purifiedcoronaviruspreparationsshowthreedifferentcate-goriesofimage:(i)'blackberry-like'virions,(ii)virionswithasmoothdepressionattheirsurface,and(iii)apparentlybrokenparticlesshowingveryclearlytheareasofspikeinsertioninthevirusmembrane.Virusprojectionsre
3、semble'mushrooms'withthe'stalk'insertedatthevirusmembrane.Amodelofthevirionstructureisproposed.CoronavirusesareagroupofenvelopedRNA-containingvirusesthathaveaunique,typicalmorphology.Theycauseavarietyofdiseasesinanimals,includingavianinfectiousbronchitis,felineinfectious
4、peritonitis,mousehepatitis,transmissiblegastroenteritisinpigs,anddiarrhoeainyoungcalves.Inhumans,theyareresponsibleforsomerespiratorydiseasesandacuteenterocolitis(forreview,seeTyrrelletal.,1975).Coronavirusvirionshaveusuallybeendescribed,afternegativestaining,aslargepleo
5、mor-phicparticlesshowingcharacteristicbulbousprojectionswhichformacoronaaroundtheviruscore(Robb&Bond,1979).Severalmeasurementshaverevealedarangeintotaldiameterofthevirionsfrom70nmto200nm.Thesurfaceprojectionshavebeenobservedtovaryinshapeandsize,althoughthelengthisnormall
6、ybetween12nmand25nm,andusuallyformasinglefringeradiatingfromtheviruscoreinallcoronaviruseswiththeexceptionofbovineentericcorona-virus(BECV)anddiarrhoeavirusofinfantmice(Sugiyana&Amano,1981),wheretwolayersofprojectionshavebeendescribed(Caul&Egglestone,1977;Robb&Bond,1979)
7、.Thedistalendsofthespikesareclearlyvisibleonthemicrographsbutthetailsareonlyoccasionallyseen.Althoughnegativestaininghaspermittedsomecriticalanalysisoftheseviruses,uncertaintyremainswithrespecttosomedetailsoftheirultrastructure,especiallyregardingtherealmor-phologyofthep
8、rojectionsandtherelationshipbetweentheprojectionsandthevirussurface.Nermut&Franck(1971)haveprovedthatwi