Analysis of the transcription strategy of the Junonia coenia densovirus (JcDNV) genome

The Junonia coenia densovirus (JcDNV) has an ambisense genome with the structural (VP) and nonstructural (NS) genes located in the 5' half on opposite strands. Northern blot analysis of Ld652 cells and Spodoptera littoralis larvae transfected with plasmid pBRJ encompassing an infectious sequence of the JcDNV genome revealed three transcripts, an unspliced 2.5 kb VP mRNA encoding capsid proteins and two NS mRNAs, one unspliced 2.5 kb mRNA encoding NS3, the other of 1.7 kb resulting from the splicing out of the NS3 coding sequence and expressing NS1 and NS2. Mapping of the transcriptional start sites revealed that VP and NS transcripts start both at 32 nt downsream of the P9 and P93 TATA boxes, respectively. The VP mRNA has a very short (3 nt) 5' untranslated region whereas the NS mRNAs have 83 nt (unspliced) and 86nt (Spliced) 5' UTR. The VP and NS transcripts co-terminate in the middle of their respective strand and possess an overlapping sequence of 61 nt at their 3' termini. Analysis of the in vivo and in vitro translation products of VP mRNA clearly showed that the 4 capsid proteins are generated by a leaky scanning mechanism.