Question

​Is the replication strategy of Sindbis virus similar/different from poliovirus? Explain thoroughly!

Answer 1

Sindbis viruses is an enveloped particle with an icosahedral capsid. It has a genome which is single stranded RNA approximately of 11.7kb long. It consists of a 5' cap and 3' polyadenylated tail which serves directly as messenger RNA (mRNA) in a host cell. Genome encodes four non-structural proteins at the 5' end and the capsid and two envelope proteins at the 3' end. This is a characteristic of all Togaviruses. Replication is cytoplasmic and rapid. The genomic RNA is translated partially at the 5’ end to produce the non-structural proteins which is then involved in genome replication and the production of new genomic RNA and a shorter sub-genomic RNA strand. This sub-genomic strand is translated into the structural proteins. The viruses assemble at the host cell surfaces and acquire their envelope through budding.

A non-coding RNA element has is found to be essential for Sindbis virus genome replication.

Poliovirus is a small, nonenveloped icosahedral virus of about 30 nm in diameter, possesses 7.5 kb +ssRNA genome whichis infectious, translated immediately upon entry inside thecell. Genome contain a 5′-nontranslated region (NTR) contains an internal ribosome entry site (IRES), followedby a single open reading frame encoding a polyprotein that is cleavedsequentially into intermediate precursors and 11 mature poliovirus proteins (Fig. 14.12). The genome is also polyadenylated at the 3′-NTR. A viral protein known as VPg (virion protein, genome-linked) associates with the 5′-end of the genome and is thought to actas a protein primer for replication of the genome.