Providence virus: a new member of the tetraviridae that infects cultured insect cells

Abstract

We identified a new member of the Tetraviridae, Providence virus (PrV), persistently infecting a midgut cell line derived from the corn earworm (Helicoverpa zea). Virus purified from these cells also productively infected a H. zea fat body cell line, and a cell line from whole embryos of the beet armyworm, Spodoptera exigua. PrV is thus the first tetravirus shown to replicate in cell culture. PrV virions are isometric particles composed of two structural proteins (60 and 7.4 kDa) that encapsidate both the genomic (6.4 kb) and the subgenomic (2.5 kb) RNAs. The monopartite organization of the PrV genome resembles that of Nudaurelia beta virus and Thosea asigna virus, members of the genus Betatetravirus. The predicted sequence of the PrV structural proteins demonstrates homology to tetraviruses in both genera. The infectivity of PrV for cultured cells uniquely permitted examination of tetravirus RNA and protein synthesis during synchronous infection. The discovery of PrV greatly facilitates studies of tetravirus molecular biology.

Genome organization and translation products of Providence virus: insight into a unique tetravirus

“…The members of the family Tetraviridae have an unusually narrow host range often restricted to only one or a few closely related lepidopteran species (Moore et al, 1985;Gordon & Hanzlik, 1998;Christian et al, 2001;Pringle et al, 2003). Tetraviruses replicate in the midgut tissues of their hosts (Moore et al, 1985;Bawden et al, 1999;Brooks et al, 2002) and sloughing of infected cells results in the stunting of infected larvae (Moore, 1991;Christian et al, 2001;Brooks et al, 2002).…”

“…have a single (monopartite) genomic RNA that encodes both replicase and VCAP often on overlapping reading frames, with VCAP translated from a subgenomic (sg) RNA (Hanzlik et al, 2005). This sgRNA may be encapsidated along with the genomic strand Pringle et al, 1999Pringle et al, , 2003. Omegatetraviral RNAs are capped at their 59 ends and are not polyadenylated, encoding instead a tRNA-like structure at their 39 ends Hanzlik et al, 1995, Du Plessis et al, 2005Yi et al, 2005).…”

“…Omegatetraviral RNAs are capped at their 59 ends and are not polyadenylated, encoding instead a tRNA-like structure at their 39 ends Hanzlik et al, 1995, Du Plessis et al, 2005Yi et al, 2005). Also betatetraviral genomic RNAs are not polyadenylated at their 39 ends, nor are they blocked at the 59 end (King & Moore, 1984;Gordon et al, 1999;Pringle et al, 2003). The tRNA-like structure has thus far only been identified at the 39 end of the type species of this genus, Nudaurelia capensis b virus (NbV).…”

“…Providence virus (PrV), which was isolated from a persistently infected Helicoverpa zea midgut cell line (MG8), is the only tetravirus known to replicate in cell culture. PrV does not appear to be very infectious, but high titres of the virus can infect H. zea fat body (FB33) cells and the virus also replicates in an embryonic Spodoptera exigua (Se-1) cell line (Pringle et al, 2003). As with the other tetraviruses, PrV particles are assembled from a single capsid protein precursor (p68), which is autoproteolytically cleaved during maturation to form the b and c peptides of 60 and 7.4 kDa, respectively.…”

“…As with the other tetraviruses, PrV particles are assembled from a single capsid protein precursor (p68), which is autoproteolytically cleaved during maturation to form the b and c peptides of 60 and 7.4 kDa, respectively. PrV particles encapsidate a genomic RNA of 6.4 kb as well as a sgRNA of 2.5 kb that encodes the viral capsid protein precursor, which has resulted in the classification of PrV as a betatetravirus (Pringle et al, 2003;Hanzlik et al, 2005). Analysis of a cDNA sequence derived from the sgRNA showed the presence of an ORF encoding a protein with predicted M r of 81 kDa, encoding a 2A-like processing site at the N terminus of the VCAP-coding sequence.…”