Recovery of infectious pariacoto virus from cDNA clones and identification of susceptible cell lines.

Pariacoto virus (PaV) is a nodavirus that was recently isolated in Peru from the Southern armyworm, Spodoptera eridania. Virus particles are non enveloped and about 30 nm in diameter and have T=3 icosahedral symmetry. The 3.0-A crystal structure shows that about 35% of the genomic RNA is icosahedrally ordered, with the RNA forming a dodecahedral cage of 25-nucleotide (nt) duplexes that underlie the inner surface of the capsid. The PaV genome comprises two single-stranded, positive-sense RNAs: RNA1 (3,011 nt), which encodes the 108-kDa catalytic subunit of the RNA-dependent RNA polymerase, and RNA2 (1,311 nt), which encodes the 43-kDa capsid protein precursor alpha. In order to apply molecular genetics to the structure and assembly of PaV, we identified susceptible cell lines and developed a reverse genetic system for this virus. Cell lines that were susceptible to infection by PaV included those from Spodoptera exigua, Helicoverpa zea and Aedes albopictus, whereas cells from Drosophila melanogaster and Spodoptera frugiperda were refractory to infection. To recover virus from molecular clones, full-length cDNAs of PaV RNAs 1 and 2 were cotranscribed by T7 RNA polymerase in baby hamster kidney cells that expressed T7 RNA polymerase. Lysates of these cells were infectious both for cultured cells from Helicoverpa zea (corn earworm) and for larvae of Galleria mellonella (greater wax moth). The combination of infectious cDNA clones, cell culture infectivity, and the ability to produce milligram amounts of virus allows the application of DNA-based genetic methods to the study of PaV structure and assembly.