Transcriptional analysis of the DNA polymerase gene of Bombyx mori parvo-like virus (China isolate).

The Bombyx mori parvo-like virus (China isolate) DNA polymerase (BmDNV-3 dnapol) gene has been tentatively identified based on the presence of conserved motifs. In the present study, we perform a transcriptional analysis of the BmDNV-3 dnapol gene using the total RNA isolated from BmDNV-3 infected silkworm at different times. Northern blot analysis with a BmDNV-3 dnapol-specific riboprobe showed a major transcript of 3.3 kb. 5'-RACE revealed that the major transcription start point was located 20 nucleotides downstream of the TATA box. In a temporal expression analysis using differential RT-PCR, BmDNV-3 dnapol transcript was detected at low levels at 6 h.p.i., increased from 6 to 36 h.p.i., and remained fairly constant thereafter. Analysis of the predicted DNA polymerase sequence using neighborjoining and protein parsimony algorithms indicated that the predicted 1115-residue polypeptide contained five motifs associated with DNA polymerases synthetic activities and three additional motifs associated with polymerases possessing 3' to 5' exonuclease activity. The molecular phylogenetic analysis of this gene supported the placement of Bombyx mori parvo-like virus in a separate virus family.