Medical Microbiology

RNAviruses 435

(virusprotein,genome-linked).Itconsistsofapproximately 7500 bases

forming 2207 codingtriplets(inthepoliovirus).Thecombinationoftheribo-

someswiththeRNAisnot,asincellularmRNA,atthecapofthe 50 end(“scan-

ningmodel”)butratherinternallyinthenontranslatedregion(NTR),whichis

about 750 nucleotideslongandispositionedbeforethecodingsegment.The

translationproductofthisRNAisaprecursorpolyproteinabout 250 kDain

size,whichisproteolyticallydividedintoabout 20 individual,functionalpro-

teinsduringorimmediatelyafteritssynthesis.TheN-terminalendofthe

polyproteincontainsthecapsidproteins,themiddleregionproteinsthatcon-

tributetotheexpressionofthestructuresrequiredforRNAreplicationand

formationoftheCPE(p.392f.)andtheC-terminalsegmentincludesproteins

ofanenzymaticcharacter(proteaseforproteolyticcleavageoftheprimary

translationproduct,seeabove,andtheRNA-dependentRNApolymerase,see

p.385)aswellasVPg,whichfunctionsasaprimerforRNAsynthesis.

Thedifferenthumanpathogenicgeneraofpicornavirusesaretheente-

roviruses,parechoviruses,hepatoviruses,andrhinoviruses.

Enteroviruses(Poliovirus,Coxsackievirus,Echovirus)

andParechoviruses

Pathogen.ThegenusEnterovirus,isolatedfromtheintestinaltract,includes

thesespecies:

— Poliovirus(poliomyelitispathogen)withthreeserotypes.

— Coxsackievirus,groupA,with 22 serotypes.

Poliovirus

1 00 nm

Fig.8. 12 Poliovirusesare 24 – 30 nminsizeand

causepoliomyelitis.

8

Kayser, Medical Microbiology © 2005 Thieme