FIG 6.

Characterization of T3-based mutant viruses expressing the #2080 VP39 protein (Ser-276) or the wild-type VP39 protein (Gly-276). (A) Light microscopic observations of BmN-4 cells infected with VP39-wt (wt) or VP39-mut (mut) at 3 dpi. (B) POLH expression. The cell lysate of BmNPV-infected cells was subjected to SDS-PAGE at 3 dpi, and a gel stained with Coomassie brilliant blue is shown. (C) Cellular BV production. The BV titer at 3 dpi was determined by plaque assay. Data are presented as the mean ± SD from triplicate experiments. *, P < 0.05, Student's t test. (D) Larval OB production. The numbers of OBs released at 4 dpi in the hemolymph of BmNPV-infected larvae were counted (n = 6). Data are presented as the mean ± SD. *, P < 0.05, Student's t test. (E) Larval BV production. The BV titer at 4 dpi in the hemolymph of BmNPV-infected larvae was determined by plaque assay (n = 6). Data are presented as the mean ± SD. *, P < 0.05, Student's t test. (F) Survival curves for B. mori larvae infected with VP39-wt or VP39-mut. The LT₅₀s of VP39-wt and VP39-mut were 104 and 126 h, respectively (n = 16). (G) Viral gene expression. BmN-4 cells were infected with VP39-wt or VP39-mut at an MOI of 5. Total RNA was reverse transcribed, and RT-qPCR of p10 and polh was performed. The data shown are the mean ± SD from triplicate experiments. (H) Viral DNA accumulation. BmN-4 cells were infected with VP39-wt or VP39-mut at an MOI of 5. Total DNA was prepared at 3 dpi and subjected to qPCR experiments. The data shown are the mean ± SD from triplicate experiments. *, P < 0.05, Student's t test. (I) BV-associated VP39 protein. A total of 100 ng of BV was subjected to Western blot analysis using anti-VP39 antibody. (J) Viral DNAs packaged in BV. The viral DNA from the same amounts of BV from VP39-wt- or VP39-mut-infected BmN-4 cells was examined by qPCR. *, P < 0.05, Student's t test.