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1、VIROLOGY190,92-l05(19%)GeneticEvolutionandTropismofTransmissibleGastroenteritisCoronavirusesCARLOSM.SANCHEZ,*FATIMAGEBAUER,*CARLOSSUNi,*ANAMENDEZ,”JOAQUiNDOPAZO,tANDLUISENJUANES**’*CentroNationaldeBiotecnologiaandCentrodeBiologi’aMolecular,CSIC-UAM,UniversidadAuthomadeMadrid,CantoBlanco,
2、28049Madrid,Spain;andtDepartamentodeSanidadAnimal,lnstitutoNationaldelnvestigacionesAgrarias,Embajadores,68,28012Madrid,SpainReceivedDecember27,1991;acceptedMay15,1992Transmissiblegastroenteritisvirus(TGEV)isanenteropathogeniccoronavirusisolatedforthefirsttimein1946.Nonenteropathogenicpo
3、rcinerespiratorycoronaviruses(PRCVs)havebeenderivedfromTGEV.Thegeneticrelation-shipamongsixEuropeanPRCVsandfivecoronavirusesoftheTGEVantigenicclusterhasbeendeterminedbasedontheirRNAsequences.TheSproteinofsixPRCVshaveanidenticaldeletionof224aminoacidsstartingatposition21.Thedeletedareainc
4、ludestheantigenicsitesCandBofTGEVSglycoprotein.Interestingly,twoviruses(NEB72andTOY56)withrespiratorytropismhaveSproteinswithasizesimilartotheentericviruses.NEB72andTOY56viruseshaveintheSprotein2and15specificaminoaciddifferenceswiththeentericviruses.Fouroftheresidueschanged(aa219ofNEB72i
5、solateandaa92,94,and218ofTOY56)arelocatedwithinthedeletionpresentinthePRCVsandmaybeinvolvedinthereceptorbindingsite(RBS)conferringenterictropismtoTGEVs.AsecondRBSusedbythevirustoinfectSTcellsmightbelocatedinaconservedareabetweensitesAandDoftheSglycoprotein,sincemonoclonalantibodiesspecif
6、icforthesesitesinhibitthebindingofthevirustoSTcells.Anevolutionarytreerelating13entericandrespiratoryisolateshasbeenproposed.Accordingtothistree,amainviruslineageevolvedfromarecentprogenitorviruswhichwascirculatingaround1941.Fromthis,secondarylineagesoriginatedPUR46,NEB72,TOY56,MIL65,BRl
7、70,andthePRCVs,inthisorder.LeastsquaresestimationoftheoriginofTGEV-relatedcoronavirusesshowedasignificantconstancyinthefixationofmutationswithtime,thatis,theexistenceofawell-definedmolecularclock.Amutationfixationrateof7+2X10e4nucleotidesubstitutionspersiteandperyearwasca
