The bovine herpesvirus alpha gene trans-inducing factor activates transcription by mechanisms different from those of its herpes simplex virus type 1 counterpart VP16.
In herpes simplex virus (HSV)-infected cells, viral gene expression is initiated when the immediate-early, or alpha, genes are transactivated by the alpha gene trans-inducing factor (alpha TIF), a component of the infecting virion. The protein binds to one or more recognition elements (TAATGARAT) in the promoters of alpha genes via interaction with the cellular proteins Oct-1 and CFF. The alpha TIF of HSV (HSV-alpha TIF) is believed to subsequently accelerate the assembly of the transcription complex by direct contact between its carboxyl-terminal acidic activation domain and at least two components of the transcription apparatus, TAFII40 and TFIIB. Like its HSV counterpart, the alpha TIF of bovine herpesvirus (BHV) (designated BHV-alpha TIF) also transactivates alpha gene promoters and for full activity exhibits a requirement for its extended carboxyl-terminal region. Despite this requirement, there is a notable lack of homology to the carboxyl-terminal acidic activation domain of HSV-alpha TIF. We swapped the amino- and carboxyl-terminal domains of HSV-alpha TIF and BHV-alpha TIF to make chimeric proteins. Using these chimeras, we show that the carboxyl terminus of BHV-alpha TIF is insufficient for transactivation, which requires cooperative determinants in both the amino-terminal and carboxyl-terminal regions of the protein. We have previously shown that the amino-terminal determinant in BHV-alpha TIF displays reduced but significant independent transactivation potential. Interestingly, this amino-terminal determinant appears not to reside in the HSV-alpha TIF, which displays no independent amino-terminal activity. Furthermore, we show that the amino-terminal activation domain of BHV-alpha TIF may be able to act synergistically with the carboxyl-terminal activation domain of HSV-alpha TIF, since a chimeric protein containing both domains appeared to be more efficient at activating transcription than either alpha TIF. In addition, the amino terminus of HSV-alpha TIF could not restore activity when linked to the carboxyl terminus of BHV-alpha TIF, while the amino terminus of BHV-alpha TIF reconstituted an intact protein with potent activation potential. We also show that in fusions with the DNA binding domain of GAL4, full activity requires the entire BHV-alpha TIF, although both amino and carboxyl termini display some activity on their own. In contrast, for HSV-alpha TIF, the carboxyl terminus is sufficient and possibly even more potent than the entire protein, while the amino-terminus is devoid of activity.(ABSTRACT TRUNCATED AT 400 WORDS)
Misra
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Department of Veterinary Microbiology, W.C.V.M. University of Saskatchewan, Saskatoon, Canada.
Walker
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Hayes
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O'Hare
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D002522:Chlorocebus aethiops; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000378:metabolism; D015967:Gene Expression Regulation, Viral; D017781:Genes, Immediate-Early; D005814:Genes, Viral; D017405:Herpes Simplex Virus Protein Vmw65 / Q000378:metabolism*; D007242:Herpesvirus 1, Bovine / Q000235:genetics / Q000378:metabolism*; D018259:Herpesvirus 1, Human / Q000378:metabolism*; D051863:Host Cell Factor C1; D007668:Kidney; D008969:Molecular Sequence Data; D050811:Octamer Transcription Factor-1; D016133:Polymerase Chain Reaction; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D035581:Transcription Factor TFIIB; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014709:Vero Cells; D014771:Virion / Q000235:genetics / Q000378:metabolism
D017931:DNA Primers; D004268:DNA-Binding Proteins; D017405:Herpes Simplex Virus Protein Vmw65; D051863:Host Cell Factor C1; D050811:Octamer Transcription Factor-1; D011993:Recombinant Fusion Proteins; D035581:Transcription Factor TFIIB; D014157:Transcription Factors