Gene activation by Varicella-zoster virus IE4 protein requires its dimerization and involves both the arginine-rich sequence, the central part, and the carboxyl-terminal cysteine-rich region.
Varicella-zoster virus (VZV) open reading frame 4-encoded protein (IE4) possesses transactivating properties for VZV genes as well as for those of heterologous viruses. Since most transcription factors act as dimers, IE4 dimerization was studied using the mammalian two-hybrid system. Introduction of mutations in the IE4 open reading frame demonstrated that both the central region and the carboxyl-terminal cysteine-rich domain were important for efficient dimerization. Within the carboxyl-terminal domain, substitution of amino acids encompassing residues 443-447 totally abolished dimerization. Gene activation by IE4 was studied by transient transfection with an IE4 expression plasmid and a reporter gene under the control of either the human immunodeficiency virus, type 1, long terminal repeat or the VZV thymidine kinase promoter. Regions of IE4 important for dimerization were also shown to be crucial for transactivation. In addition, the arginine-rich domains Rb and Rc of the amino-terminal region were also demonstrated to be important for transactivation, whereas the Ra domain as well as an acidic and bZIP-containing regions were shown to be dispensable for gene transactivation. A nucleocytoplasmic shuttling of IE4 has also been characterized, involving a nuclear localization signal identified within the Rb domain and a nuclear export mechanism partially depending on Crm-1.
Baudoux
L
L
Laboratory of Fundamental Virology and Immunology, Institute of Pathology B23, University of Liege, B-4000 Liege, Belgium.
Defechereux
P
P
Rentier
B
B
Piette
J
J
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001120:Arginine; D003545:Cysteine; D019281:Dimerization; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D005982:Glutathione Transferase / Q000235:genetics; D016325:HIV Long Terminal Repeat; D015497:HIV-1 / Q000235:genetics; D006367:HeLa Cells; D014645:Herpesvirus 3, Human / Q000235:genetics*; D006801:Humans; D017874:Immediate-Early Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016366:Open Reading Frames; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation; D014162:Transfection; D014764:Viral Proteins
D017874:Immediate-Early Proteins; C085824:ORF4 protein, Human herpesvirus 3; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D015534:Trans-Activators; D014764:Viral Proteins; D001120:Arginine; D005982:Glutathione Transferase; D003545:Cysteine