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J Virol, May 1998, p. 4049-4056, Vol. 72, No. 5
Department of Microbiology, Columbia
University, New York, New York 10032
Received 7 October 1997/Accepted 9 February 1998
The adenovirus gene regulatory program occurs in two distinct
phases, as defined by the onset of DNA replication. During the early
phase, the E1A, E1B, E2, E3, and E4 genes are maximally expressed,
while the major late promoter (MLP) is minimally expressed and
transcription is attenuated. After the onset of DNA replication, the
IVa2 and pIX genes are expressed at high levels, transcription from the
MLP is unattenuated and fully activated, and early gene expression is
repressed. Although the cis elements and
trans-acting factors responsible for the late-phase
activation of the MLP have been identified and characterized and the
role of DNA replication in activation has been established, the
mechanism(s) underlying the commensurate decrease in early gene
expression has yet to be elucidated. The results of this study
demonstrate that this decrease depends on a fully functional MLP.
Specifically, virus mutants with severely deficient transcription from
the MLP exhibit a marked increase in expression of the E1A, E1B, and E2
early genes. These increases were observed at the level of
transcription initiation, mRNA accumulation, and protein production. In
addition, expression from the late gene pIX, which is not contained
within the major late transcription unit (MLTU), is also markedly
increased. To begin the analysis of the mechanisms underlying these
late-phase effects, mixed-infection experiments with mutant and
wild-type viruses were performed. The results show that the effects on
early gene expression, as measured both at the protein and RNA levels, are mediated in trans and not in cis. These
observations are consistent either with a model in which one or more
late protein products encoded by the MLTU acts as a repressor of early
gene expression or with one in which the wild-type MLP competes with
early promoters for limiting transcription factors.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Control of Adenovirus Early Gene Expression
during the Late Phase of Infection
*
Corresponding author. Mailing address: Department of
Microbiology, Columbia University, HHSC 1308, 701 W. 168th St., New
York, NY 10032. Phone: (212) 305-4179. Fax: (212) 305-1468. E-mail: csy1{at}columbia.edu.
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