The Subviral Agents

Abstract

This chapter focuses on satellites and other virus-dependent nucleic acids. Satellites are subviral agents that lack genes that could encode functions needed for replication. Thus for their multiplication they depend on the coinfection of a host cell with a helper virus. Satellite genomes have a substantial portion or all of their nucleotide sequences distinct from those of the genomes of their helper virus. The satellite viruses encode a structural protein that encapsidates their genome and so have nucleoprotein components distinct from those of their helper viruses. Satellite nucleic acids encode either nonstructural proteins, or no proteins at all, and are encapsidated by the CP of helper viruses. Satellite-like nucleic acids resemble satellites because they do not encode a replicase but differ because they encode a function necessary for the biological success of the associated virus. They can therefore be considered as components that remedy a deficiency in a defective virus. The genomes of most satellites have short sequences, often at the termini, that are identical to the genome of the helper virus. This is presumably linked to the dependence of nucleic acids of both satellite and helper virus on the same viral polymerase and host-encoded proteins for replication. Five subgroups of satellite viruses are currently distinguished, which include chronic bee-paralysis virus-associated satellite virus, satellites that resemble tobacco necrosis satellite virus, and nodavirus-associated satellite virus. The virus-dependent nucleic acids include a diverse range of DNA and RNA molecules that do not encode a capsid protein, but are packaged in capsids encoded by their helper virus.