SEQUENCE OF RNA2 OF THE HELICOVERPA-ARMIGERA STUNT VIRUS (TETRAVIRIDAE) AND BACTERIAL EXPRESSION OF ITS GENES

The complete nucleotide sequence of RNA2 of Heli-coverpa armigera stun t virus (HaSV), a member of the Tetraviridae, was determined by charac terization of cloned cDNA and PCR products and direct sequencing of ge nomic RNA. The capped, positive sense, single-stranded RNA is 2478 nuc leotides in length and has two overlapping open reading frames (ORFs) likely to be cistrons which are situated between terminal non-coding r egions of 282 and 168 bases, 5' and 3', respectively. Extensive second ary structure of the RNA strand is indicated, including a tRNA-like st ructure at the 3' terminus which is the first such structure discerned in an animal virus. The first ORF encodes a 17 kDa PEST protein (p17) of unknown function while the second ORF encodes the 71 kDa coat prot ein precursor (p71) that is cleaved at an Asn-Phe site into the 64 kDa and 7 kDa coat proteins. The precursor coat protein is 66% identical to that of another tetravirus, the Nudaurelia omega virus, with most o f the difference residing in a 165 amino acid region located in the mi ddle of the sequence. Despite the extensive similarity, no serological relationship was observed between the two viruses, suggesting that th e dissimilar region is exposed on the capsid exterior. Expression in b acteria of the two RNA2 gene products shows they are likely to be expr essed by a leaky scan-through mechanism. Bacterial expression of p71 d id not produce virus-like particles while expression of p17 produced l arge arrays of mostly hollow, hexagonal tube-like structures.