Identification, transcriptional and phylogenetic analysis of the DNA polymerase gene of Pieris rapae granulovirus.

The DNA polymerase gene (dnapol) of the Pieris rapae granulovirus (PiraGV) was completely sequenced and located between 73.1 and 76 m.u. on the PiraGV genome. Its open reading frame (ORF) has 3135 nucleotides (35% G-C content) encoding 1045 amino acids with a predicted molecular mass of 122.16 kDa. Homology analysis indicated that PiraGV dnapol had 28-66% amino acid identity to that of other known baculoviruses. Comparative sequence analyses demonstrated that the PiraGV dnapol gene contains conserved 3'-5' exonuclease motifs and DNA binding functional domains of the DNA polymerase enzyme found in all known baculovirus dnapols. Northern blot results showed that in infected Pieris rapae larvae the PiraGV dnapol gene was transcribed as a predominant 3.7 kb mRNA. 5' and 3' RACE indicated that the PiraGV dnapol transcript was initiated from the thymine residue located at -378 nt upstream from the ATG start codon and terminated at the polyadenylation signal AATAAA. Phylogenetic analysis of dnapol sequences suggests that the PiraGV dnapol is more closely related to that of Cydia pomonella GV and Cryptophlebia leucotreta GV than to those of other baculoviruses.