Virology
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	Spring, 2004 Lecture Outline 3/16 DOUBLE-STRANDED RNA VIRUSES   Reo-, Birna-, Cysto- [phage f6], Partiti- viridae Reoviridae: infect wide host range as grp: plants, insects, mammals many in grp cause serious Dz & have economic impact ds RNA 1st detected; 6 genera not closely related structure: double shelled, no envelope [no lipid]- appear spherical UNIQUE- core contains 10-12 molecules of ds RNA 15 x 106 d- genomic RNA also in core- RNA-directed RNA polymerase transcription & replication: in cytoplasm of host ds RNA inactive as mRNA UNIQUE: "conservative" mode- nascent strand copied from one strand; then released [contrasts c partitiviruses] products- sigma-1 is hemagglutinin: cell attachment sigma-2 read in different frame of same mRNA S1 RNA therefore is bicistronic "eukaryotic mRNA as always monocistronic"- a crumbling thought reassortment: dsRNA never free, always protein bound minichromosomes do however rearrange -> new strains as in flu Birnavirus: this genus has only two segments of RNA; replication appears similar to reo's Cystoviridae c one member- Phage f6 specific for Pseudomonas phaseolicola only known phage c intracore transcriptase activity [like reo's] structure: 3 RNA segments- 5 x 106 d single capsid layer- contains 5 proteins & dsRNAs transcription: semiconservative- nascent strand replaces plus strand plus strand released as mRNA [contrasts c reo's] Partitiviridae: family for some fungal viruses semiconservative as in phage f6 disease examples Reovirus diseases Rotaviral Dz: acute gastroenteritis- worldwide in children 6-24 m old a leading cause of death in developing countries Colorado tick fever- orbivirus largest genome of dsRNA grp; only tick-borne virus in US symptoms & epidemiology   Next up: Retroviruses & reverse transcriptase
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