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J Virol. 1994 Apr;68(4):2108-17.

A human cytomegalovirus early promoter with upstream negative and positive cis-acting elements: IE2 negates the effect of the negative element, and NF-Y binds to the positive element.

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  • 1Department of Microbiology, School of Medicine, University of Iowa, Iowa City 52242.


The human cytomegalovirus early promoter for the UL4 gene, which codes for an early viral envelope glycoprotein designated gpUL4, requires immediate-early viral protein two (IE2) synthesis to be activated (C.-P. Chang, C. L. Malone, and M. F. Stinski, J. Virol. 63:281, 1989). We investigated the cis-acting and trans-acting factors that regulate transcription from this UL4 promoter. In transient transfection assays, the viral IE2 protein negated the effect of an upstream cis-acting negative element and enhanced downstream gene expression. A cis-acting positive element contributed to the activity of the viral promoter when an upstream cis-acting negative element was deleted or when the viral IE2 protein was present. The cellular protein(s) that binds to the cis-acting negative element requires further investigation. The cellular protein that binds to the cis-acting positive element was characterized. Two DNA sequence-specific protein complexes were detected with DNA probes spanning the region containing the cis-acting positive element and human cytomegalovirus-infected human fibroblast cell nuclear extracts. The more slowly migrating complex was labeled complex A, and the faster was labeled complex B. Only complex B was detected with mock-infected cell nuclear extracts. Competition experiments confirmed the specificity of the A and B complexes. The protein bound to the DNA in both the complexes contacts a CCAAT box imperfect dyad symmetry (5'CCAATCACTGG3'). Either CCAAT box within the dyad symmetry could compete for binding the nuclear factor. Mutation of the CCAAT box dyad symmetry resulted in a decrease of the transcriptional activity from the UL4 promoter. A cellular transcription factor, antigenically related to nuclear factor-Y (NF-Y), was found in both complexes A and B. Events associated with viral infection caused phosphorylation of protein complex A. Dephosphorylation of the DNA-binding protein converts complex A to complex B. The effect of phosphorylation of NF-Y is not known.

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