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1、ArchVirol128(1993)XTTITVirologyDivisionNews￥JL.J.&.~GenusTorovirusassignedtotheCoronaviridaeAtitsApril1992mid-termmeeting,theExecutiveCommitteeofICTVacceptedaproposalfromtheCoronaviridaeStudyGroupthatthegenusTorovirus,previouslyunassignedtoafamily,shouldjointhegenus
2、CoronavirusintheCoronaviridae.Thiswasinrecognitionofthemanycharacteristicssharedbythesetwogenera,mostofthesimilaritieshavingcometolightonlyrecentlywiththesequencingofalargepartofthegenomeofBernevirus,thetypespeciesandmostthoroughlystudiedtorovirus.Bothgeneracomprise
3、viruseswhichareenvelopedandhaveprominentspikes(S)comprisingglycopolypeptidesof~200kDawhichexhibitacoiled-coilstructureinthecarboxy-terminal,membrane-anchoringhalt:Eachviruspossessesanintegralmembraneprotein(M)(~25kDa)withthreemembrane-spanningsequencesintheamino-ter
4、minalhalf.Thegenomesaresingle-stranded,non-segmented,positive-senseRNAsof~30kb,thefirsttwo-thirdsbeingthegene(number1)whichencodesthepresumptiveRNA-dependentRNApotymerase.Gene1encodestwooverlappingopenreadingframes(ORFs),1aand1b,ribosomalframeshiftingbeingin-volvedi
5、nthetranslationofthesecondORF.FiveormoresubgenomicmRNAsaregeneratedforminga3'co-terminalnestedset.Onlythe5'sequencenotpossessedbythenextsmallermRNAistranslated.Overallgenomeorganisationissimilar,thegeneorderbeing5'-pol-S-M-N-3',whereNisthenucleocapsidprotein.Therear
6、eadditionalgenes,someofwhicharenotcommonbetweenthetwogeneraand,indeed,notpossessedbyallmembersofonegenus,e.g.,thehaemagglutinin-esteraseglycoproteinofsomecoronaviruses.Anumberoffeaturesrequirethatthecoronavirusesandtorovirusesshouldbeinseparategenera.Thereisvirtuall
7、ynosequencesimilaritybetweenthetwogroups.TheNproteinsdiffergreatlyinsize(,-~60kDaforcoronaviruses,18kDafortoroviruses)andformdif-ferentlyshapednucleocapsids.Thevirusesareofsimilarsize,about130nmindiameter,thecoronavirusesbeingpleomorphicbutroughlysphericalinshape,an
8、dinnegatively-stainedpreparationstorovirusescanlookverysimilartocoronaviruses.However,inultra-thinsectionstorovirusesexhibitdisc-,kidney-o
