In vitro characterization of a Trichoplusia ni single nucleocapsid nuclear polyhedrosis virus.

A Trichoplusia ni single nucleocapsid nuclear polyhedrosis virus (TnSNPV) isolate was cloned and its replication studied in the BTI-Tn-5B1-4 insect cell line. The BTI-Tn-5B1-4 cells were highly susceptible to TnSNPV infection, with 99% of the cells containing viable polyhedra by 30 h post-inoculation. Viral DNA synthesis was detected by 9 h post-infection (p.i.). Infectious budded virus (BV) was first detected at 13 h p.i. and reached an average maximum titre of 3.875 x 10(6) p.f.u./ml 27 h p.i. A total of 25 BV structural proteins having apparent molecular masses ranging from 27.5 kDa to 86 kDa were identified. Using [35S]methionine pulse-labelling, 19 virus-induced proteins with molecular masses ranging from 27 kDa to 106 kDa were detected from 4 to 28 h p.i. Host cell protein synthesis continued throughout virus replication, although at gradually decreasing rates. Thirty-two structural proteins of occlusion-derived virus ranging in apparent molecular masses from 11 kDa to 98 kDa were identified using silver staining procedures. Digestion of viral DNA with the restriction endonucleases EcoRI, HindIII and BamHI generated 31, 26 and 12 fragments, respectively. Estimates for the molecular mass of the TnSNPV genome ranged from 115.5 to 119.2 kbp. In bioassays performed with neonate T. ni larvae, the mean LD50s for the TnSNPV and Autographa californica MNPV were 1.5 (+/- 0.3) and 11.0 (+/- 4.0) polyhedra per larva, respectively.