The baculovirus cg30 gene is present in the genomes of most alphabaculoviruses. The gene product,
CG30, contains two putative functional domains, a RING finger motif and a leucine zipper motif. A geneknockout
study in Autographa californica nucleopolyhedrovirus (AcMNPV) revealed that a cg30-disrupted
virus did not show any striking differences compared with wild-type virus. To determine the roles of
cg30 in another alphabaculovirus, we constructed two Bombyx mori NPV (BmNPV) mutants lacking a
functional cg30 by lacZ cassette insertion and characterized its infectivity in BmN cells and B. mori larvae.
The mutants produced fewer budded viruses (BVs) in BmN cells and B. mori larvae compared with wildtype
BmNPV. We also observed a decrease in the release of occlusion bodies (OBs) in the hemolymph of
the larvae infected with the cg30 mutants. To investigate the role of a RING finger domain of CG30 during
virus growth, we further constructed two mutants; one expressed a mutant CG30 where a RING finger
motif is disrupted by a single amino acid substitution, whereas the other possessed a CG30 derivative
that completely lacked the RING finger domain. Both produced fewer OBs in the hemolymph of B. mori
larvae, demonstrating that a RING finger domain of CG30 is involved in maximum OB production in
the hemolymph of B. mori larvae. We also revealed that CG30 is expressed as a nuclear protein with a
molecular mass of 30 kDa in BmNPV-infected cells.