Increasing the Capping Efficiency of the Sindbis Virus nsP1 Protein Negatively Affects Viral Infection

Alphaviruses are arthropod-borne RNA viruses that cause severe disease and are a significant burden to public health. Alphaviral replication results in the production of capped and noncapped viral genomic RNAs, which are packaged into virions during infections of vertebrate and invertebrate cells. However, the roles that the noncapped genomic RNAs (ncgRNAs) play during alphaviral infection have yet to be exhaustively characterized. Here, the importance of the ncgRNAs to alphaviral infection was assessed using mutants of the nsP1 protein of Sindbis virus (SINV), which alter the synthesis of the ncgRNAs by modulating the protein's capping efficiency. Specifically, point mutants at residues Y286A and N376A decreased capping efficiency, while a point mutant at D355A increased the capping efficiency of the SINV genomic RNA during genuine viral infection. Viral growth kinetics were significantly reduced for the D355A mutant relative to wild type infection, whereas the Y286A and N376A mutants showed modest decreases in growth kinetics. Overall genomic translation and nonstructural protein accumulation was correlated with increases and decreases in capping efficiency. However, genomic, minus strand, and subgenomic viral RNA synthesis w...Continue Reading