Formation of Bombyx mori nucleopolyhedrovirus IE2 nuclear foci is regulated by the functional domains for oligomerization and ubiquitin ligase activity.
Baculovirus IE2 functions as a transregulator and is also involved in viral DNA replication. However, the mechanism for these functions remains unknown. It has previously been reported that Bombyx mori nucleopolyhedrovirus (BmNPV) IE2 has a ubiquitin ligase activity that is dependent on the RING finger domain and that IE2 can oligomerize through its C-terminal coiled-coil region. Here, confocal microscopy analysis demonstrated that IE2 formed nuclear foci only during the early phase of infection (2-6 h post-infection). Therefore, it was determined whether the IE2 functional regions described above could affect this characteristic distribution. Transient expression of ie2 also showed focus formation, suggesting that IE2 does not require any other viral factors. IE2 mutants lacking the C-terminal coiled-coil region did not form foci, while a mutant of the RING finger domain showed nuclear foci that appeared larger and brighter than those formed by wild-type IE2. In addition, IE2 exhibited enlarged foci in infected cells following treatment with a proteasome inhibitor, suggesting that foci enlargement resulted from accumulation of IE2 due to inhibition of the ubiquitin-proteasome pathway. These results suggest that BmNPV IE2 oligomerization and ubiquitin ligase activity functional domains regulate nuclear foci formation.
Imai
Noriko
N
Molecular Entomology Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan.
Matsumoto
Shogo
S
Molecular Entomology Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan.
Kang
WonKyung
W
Molecular Entomology Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan.
D000818:Animals; D012831:Bombyx / Q000821:virology*; D002460:Cell Line; D004279:DNA, Viral / Q000096:biosynthesis*; D017874:Immediate-Early Proteins / Q000378:metabolism*; D008025:Ligases / Q000378:metabolism* / Q000502:physiology; D017924:Nucleopolyhedroviruses / Q000235:genetics / Q000502:physiology*; D014779:Virus Replication
D004279:DNA, Viral; D017874:Immediate-Early Proteins; D008025:Ligases