G. V. Devi-Rao,1,
M. K. Rice,1 L. W. Gary,2 D. C. Bloom,2 R. M. Sandri-Goldin,3 P. Ghazal,4 and E. K. Wagner1*
Department of Molecular Biology and Biochemistry,1 Department of Microbiology and Molecular Genetics and Center for Virus Research, University of California, Irvine, California,3 Department of Molecular Genetics & Microbiology, University of Florida College of Medicine, Gainesville, Florida,2 Genomic Technology and Informatics Centre, University of Edinburgh Medical School, Edinburgh, United Kingdom4
Received 11 February 2004/ Accepted 28 May 2004
We constructed a promoter mutation altering the immediate-early expression of the herpes simplex virus type 1 (HSV-1) ICP27 transcript and its cognate wild-type rescue viruses in order to assess the role of the ICP27 protein in the earliest stages of viral infection by global transcriptional analysis with a DNA microarray. This mutant, ICP27/VP16, replaces the whole ICP27 promoter/enhancer with the VP16 promoter. It demonstrates loss of immediate-early expression of ICP27 according to the criteria expression in the absence of de novo protein synthesis and earliest expression in the kinetic cascade. Significant differences in relative transcript abundances between the mutant and wild-type rescue viruses were limited at the earliest times measured and not evident at all by 4 h after infection. Consistent with this observation, levels of some critical proteins were reduced in the mutant as compared to rescue virus infections at the earliest times tested, but were equivalent by 8 h postinfection. Further, both single and multistep levels of virus replication were equivalent with both mutant and rescue viruses. Thus, altering the immediate-early kinetics of ICP27 leads to a suboptimal quantitative lag phase in gene expression but without consequence for replication fitness in vitro. Infections in vivo also revealed equivalent ability of mutant and rescue viruses to invade the central nervous system of mice following footpad injections. Limitations to an immediate-early role of ICP27 in the biology of HSV are discussed in light of these observations.
A. Sun and G. V. Devi-Rao contributed equally to this work.
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