Variants of open reading frame Bm126 in wild-type Bombyx mori nucleopolyhedrovirus isolates exhibit functional differences.

The open reading frame (ORF) 126 (Bm126) of Bombyx mori nucleopolyhedrovirus (BmNPV) is a homologue of Ac150 and belongs to the baculovirus 11K protein family. Bm126 was amplified from BmNPVs isolated from five different regions of China. Sequence analysis showed that the isolates had two different subtypes of Bm126, Bm126-SX and Bm126-GD, and both were different from that of the BmNPV T3 isolate. All of the BM126 ORFs contained a hydrophobic N terminus and a C6 motif at their C terminus, but the sequence between the N terminus and C6 motif varied in each isolate. The function of Bm126 was studied using bacmid BmBacJS13 derived from a BmNPV containing Bm126-SX. A 3' rapid amplification of cDNA ends showed that the transcript of Bm126 was first detected at 6 h post-infection. A Bm126-knockout bacmid was constructed in which the majority of the coding region of Bm126 was deleted. Subsequently, the gene was repaired with Bm126-SX or Bm126-GD and tested for infectivity. The deletion of Bm126 had no obvious effect on the budded virus growth curve and the mean lethal dose of the occlusion bodies (OBs); however, the mean survival time of the larvae infected with Bm126-null virus was significantly delayed compared with that of the control virus. The delay was rescued by repairing the deletion with Bm126-SX but not with Bm126-GD. In addition, the virus repaired with Bm126-GD showed a significant increase in OB yield, both in vitro and in vivo.