The translational and transcriptional initiation sites of BmNPV lef-7 gene

Abstract

The predicted open reading frame of lef-7 from Bombyx mori nucleopolyhedrovirus (BmNPV) is 45 bp longer at the 5'-terminal and harbors a 42 bp deletion towards the 3' terminal end compared to that of Autograph californica mlulticapsid NPV (AcMNPV). In the present study, to determine whether the BmNPV lef-7 is translated from an initiation site different from that of AcMNPV lef-7, the translational and transcriptional initiation sites of BmNPV lef-7 were examined. A BmNPV mutant, Bmlef7M1(-) was constructed by deleting 11 nucleotides (nt) including the predicted initiation codon ATG. Western blot analysis demonstrated that the size of LEF-7 in BmNPV and Bmlef7M1(-)-infected cells was identical. The LEF-7s in BmNPV and Bmlef7M1(-)-infected cells were both localized in the nuclei as observed using confocal microscopy. Therefore, the presumed initiation codon ATG (at 97059 nt of BmNPV genome) appears to be non-functional for lef-7 translation. The 5'-RACE analysis revealed that transcription of lef-7 mRNA in BmNPV and Bmlef7M1(-)-infected cells both initiated from an ATCATT motif located 26 nt upstream of the second ATG (located at 97014 nt on BmNPV genome), and 20 nt downstream of the presumed initiation codon.