agent commonly known human member family composed protein single stranded positive sense long viral particle diameter symmetry short simple composition non protein coat widely regarded simplest significant virus isolated published different teams researchers mit characterized useful model system understanding biology cycle human cells binding like known cell surface interaction change viral particle necessary viral entry attached host cell membrane entry viral acid thought occur ways formation membrane injected host cell virus taken recent experimental evidence supports hypothesis suggests taken immediately particle viral released positive stranded virus enclosed viral particle messenger immediately translated host cell entry virus cell translation machinery causing cellular protein synthesis favor virus specific protein production unlike host cell end extremely long highly structured region viral called internal entry site discovered found directs translation viral genetic region prevent viral protein production translated long auto internal approximately individual viral proteins problem production refers equal amounts protein produced needed amounts structural control process regulation occur individual viral proteins include seen dependent function multiple copies viral viral small protein viral necessary synthesis viral positive negative strand proteins comprise protein complex needed virus proteins viral translation involve single process synthesis realized order replicated multiple copies synthesis association molecules consisting template growing varying length seen complexes strand synthesis small protein group acting element located stem loop virus molecules synthesis function destined assembly new virus particles packaging survive outside host cell including respectively copies termini form interior surface assemble form outer surface consisting termini form time copies copy virus attached end fully assembled leaves confines host cell hours following initiation infection cells mechanism viral release cell unclear dying cell release drake demonstrated able undergo light allowed undergo multiple host cells viable formed virus single origin structurally similar human use like molecules recognize enter host cells phylogenetic analysis protein sequences suggests evolved cluster virus ancestor arose distinct probably occurred result change cellular cluster leading change allowing virus nervous tissue rate virus relatively high virus synonymous rate site year non synonymous rate site year base distribution non random common expected end higher end use non random ending favoured ending avoided use differs appears driven selection slightly different protein proteins define cellular virus common form encountered nature forms extremely infectious november wild highly localized regions pakistan afghanistan wild declared september detected october india november wild seen detection parts nigeria pakistan specific strains prepare inactive prepared wild reference strains oral contains live weakened strains virus strains monkey kidney cells introduces viral ability virus nervous tissue classified distinct species belonging genus family species eliminated genus assigned species human later renamed genus family type species genus changed human primary infection virus ability enter cell produce additional infectious particles presence thought define animals tissues infected found outside laboratories cells humans higher strictly human naturally species infected gene appears subject positive selection protein domains domain contains virus binding site domain responsible binding virus infection occurs oral route meaning virus viral occurs tract virus shed infected individuals cases primary presence virus occurs infection cases virus spreads sites brown fat tissue muscle sustained viral causes secondary leads development minor symptoms fever sore throat occurs disease occurs virus enters central nervous system motor spinal cord brain stem motor resulting selective destruction motor leading temporary permanent rare cases leads respiratory arrest death cases disease muscle pain frequently observed prior onset weakness typically days weeks prior recovery respects phase infection thought accidental diversion normal infection mechanisms enters poorly understood non mutually exclusive suggested explain entry theories require primary hypothesis pass directly blood central nervous system crossing blood brain barrier independent second hypothesis suggests transported peripheral tissues blood example muscle tissue spinal cord nerve pathways transport hypothesis virus imported infected disease central nervous system believed present surface human cells expression explain certain tissues suggests tissue determined cellular infection recent work suggested type response specifically alpha beta important factor defines types cells support mice expressing genetic engineering lacking type expanded repertoire tissue types mice able infected virus immune system avoidance uses key mechanisms evade immune system capable surviving highly acidic conditions tract allowing virus host spread body system second replicate quickly virus host organs immune response mounted detail given attachment phase surface virus attachment sites located pockets canyon bases narrow access virus attachment sites protected host immune surveillance remainder surface avoid host immune response individuals exposed infection develop immunity immune individuals present tract specifically able block prevent spread virus motor central nervous system infection provide immunity second attacks individual extremely rare mouse humans known natural hosts infected long study small animal model developed laboratories mice engineered express human unlike normal mice mice susceptible injected injected directly spinal cord brain infection mice signs resemble humans central nervous systems paralyzed mice similar humans mouse model human infection proven tool understanding biology distinct types mice studied mice human incorporated mouse mice express highest levels highest sensitivity mice susceptible pathways oral route mice incorporated human mice susceptible infection route possibly express decreased levels mice shown susceptible infection useful infection model mice human located mice exhibit lowest levels expression susceptible infection recently fourth mouse model developed mice carry driven promoter proven susceptible routes addition mice capable developing form development mouse profound effect oral production previously monitoring safety performed susceptible virus approved use mouse alternative method assessing effectiveness mouse model approved tests synthesis baltimore dna technology generate infectious clone animal virus dna introduced cells infectious produced creation infectious clone propelled understanding biology standard technology study group succeeded chemical code producing world synthetic virus scientists converted published sequence bases long dna sequence dna easier short fragments dna sequence obtained mail order assembled complete viral assembled gene synthesis company process took years nineteen markers incorporated synthesized dna distinguished natural convert dna natural state translate producing functional viral particle newly synthetic virus injected mice determine synthetic version able cause disease synthetic virus able replicate cause death mice synthetic version times lethal original virus modification modification virus called recently early clinical trials treating cancer
Poliovirus