Arch Virol (2003) 148: 1413–1418
Identiﬁcation of a repressor of late gene expression
within the AcMNPV genome
K. L. Hefferon
Cornell Research Foundation, Ithaca, New York, U.S.A.
Received March 15, 2002; accepted March 3, 2003
Published online June 2, 2003
Summary. Viral replication and late gene expression of Autographa californica
multiple nucleopolyhedrovirus (AcMNPV) requires a series of late expression
factors. We examined the AcMNPV genome for additional factors which affect
late gene expression. During these investigations, a segment of the AcMNPV
genome located immediately downstream to LEF-7 was found to possess a re-
pressor activity. Elimination of this region resulted in greatly enhanced late gene
expression. We were unable to link repressor activity to a single open reading
frame, suggesting that a cis-acting element rather than a trans-acting factor is
responsible for this phenomenon.
Autographa californica multiple nucleopolyhedrovirus, (AcMNPV) is the type
species of genus Nucleopolyhedrovirus, family Baculoviridae, a family of large
double-stranded DNA viruses with a circular genome . Baculoviruses are
known to infect a broad spectrum of organisms including insects and crustaceans.
During the virus life cycle, AcMNPV orchestrates several tiers of temporally-
controlled gene expression. Early gene expression takes place prior to replication
and requires a host-derived α-amanitin sensitive RNA polymerase. Late and very
late gene expression take place after viral DNA replication, and involve a virus-
derived RNA polymerase .
Nineteen LEFs have now been identiﬁed as playing a role in AcMNPV repli-
cation and late gene expression . These include the replication LEFs (LEF-1,
LEF-2, LEF-3, LEF-7, P143, P35, DNApol, IE1 AND IE2) which are involved in
forming the replication complex and preparing the cell for viral replication, and
the transcription LEFs (LEF-4, LEF-5, LEF-6, LEF-8, LEF-9, LEF-10, LEF-11,
LEF-12, P47, P39) which are required for transcription of late genes [10, 17–19].
Very late expression factor 1, or VLF-1, is essential for expression of genes such
as p10 very late in the infection process .