Core-associated genome replication mechanisms of dsRNA viruses

Abstract

The double-stranded RNA (dsRNA) viruses are a diverse group, which infect a wide assortment of prokaryotic and eukaryotic hosts. Although not all dsRNA viruses are considered pathogens, many cause devastating disease in their hosts and have widespread medical, veterinary, and agricultural impacts. Currently, the International Committee for the Taxonomy of Viruses (ICTV) recognizes seven distinct families of dsRNA viruses (Hypoviridae, Totiviridae, Birnaviridae, Partitiviridae, Cystoviridae, Chrysoviridae, and Reoviridae) (Table 11.1) (http://phene.cpmc.columbia.edu). Of these families, Reoviridae is composed of the largest number of individual species, which are categorized into 12 separate genera, and includes some of the most severe dsRNA viral pathogens of humans and domestic animals (Mellor and Boorman, 1995; Parashar et al., 2003). In particular, rotaviruses are members of the Reoviridae family and a leading cause of lethal gastroenteritis in young children and infants (Parashar et al., 2003). As such, the Reoviridae family has been studied in detail, providing insights into the general strategies dsRNA viruses use to propagate. Members of the Totiviridae and Cystoviridae families, which infect fungi and bacteria, respectively, have replication strategies similar to Reoviridae and are often viewed as models for understanding dsRNA virus biology (Mindich, 2004; Poranen and Tuma, 2004; Wickner, 1996). Together, studies of these three virus families have elucidated several common themes in dsRNA virus replication: (i) RNA synthesis occurs within a protected core via an anchored RNA-dependent RNA polymerase (RdRp); (ii) genome replication and capsid assembly occur simultaneously; and (iii) cis-acting elements in the viral RNA determine template specificity. This chapter will explore these themes regarding the core-associated genome replication of dsRNA viruses by reviewing structural and biochemical studies of individual members of Totiviridae, Cystoviridae, and Reoviridae families.