Nidovirales

This chapter focuses on the Nidovirales order whose member families include Arteriviridae, Coronaviridae, and Roniviridae. The nidoviruses genome is an infectious, linear, positive sense RNA molecule, which is capped and polyadenylated. Based on the genome size, they are divided into two groups large and small nidoviruses. The genomes of the large nidoviruses are well over 25 kb in length with size differences in the 5 kb range. Based on the genome size, they can be distinguished into two groups, large and small nidoviruses. The genomes of the large nidoviruses are well over 25 kb in length with size differences in the 5 kb range. Although the structural proteins of the nidoviruses are generally functionally equivalent, there is no firm indication that any single protein species is evolutionary conserved across all of the families. Members of the family Coronaviridae generally possess three or four envelope proteins. The most abundant one is the membrane (M) protein. Though different in sequence, the M proteins of corona-, toro-, and bafiniviruses are alike in size, structure, and presumably also in function. Nidoviruses have lipid envelopes, which are commonly acquired by budding at membranes of the endoplasmic reticulum, intermediate compartment and/or Golgi complex. In coronaviruses, the S protein is an important target for T cell responses and is the major inducer of virus-neutralizing antibodies, which are elicited by epitopes located mostly in the N-terminal half of the molecule.