Affiliation:
1. Laboratory of Molecular Entomology and Baculovirology, RIKEN (The Institute of Physical and Chemical Research), Wako,1 and
2. Core Research for Evolutional Science and Technology (CREST) Project, Japan Science and Technology Corporation, Kawaguchi,2 Japan
Abstract
ABSTRACT
The baculovirus
Bombyx mori
nucleopolyhedrovirus (BmNPV) contains five related open reading frames (ORFs). Recent sequence analyses of several other baculovirus genomes reveal that these ORFs belong to a unique multigene family called the baculovirus repeated ORFs (
bro
) family. Here we have characterized these five genes from BmNPV at the transcriptional and translational levels. Reverse transcription-PCR and primer extension analyses indicated that transcription of all
bro
genes occurs by 2 to 4 h postinfection (p.i.) and reaches maximal levels between at 8 and 12 h p.i. Transcription of all genes is initiated between 50 and 70 nucleotides upstream of the start codon, at a characteristic C(T)AGT motif. Expression of a
cat
reporter gene under the control of each
bro
promoter provides evidence that a viral factor(s) is required for the transcription of all
bro
genes. Immunoblot analysis indicated that a population of BRO proteins is produced vigorously between at 8 and 14 h p.i. Immunohistochemical analysis by confocal microscopy showed that BRO proteins are localized in both the nucleus and the cytoplasm at 8 h p.i. Four BmNPV mutants, in which the
bro-a
,
bro-b
,
bro-c
, and
bro-e
genes were individually inactivated, were successfully isolated. However, exhaustive efforts failed to isolate a
bro-d
-deficient mutant. Similarly, it was not possible to isolate a double-deletion
bro-a bro-c
mutant. The
bro-d
gene may play an irreplaceable functional role(s) during viral infection, while
bro-a
and
bro-c
may functionally complement each other.
Publisher
American Society for Microbiology
Subject
Virology,Insect Science,Immunology,Microbiology