Tax

Transcriptional activator that governs the viral transcription from the 5'LTR via the recruitment of dimers of host phosphorylated CREB1. Together they bind cAMP response elements within the viral promoter and mediate high-level viral transcription. Increases host CREB1 O-GlcNAcylation to further increase 5'LTR transactivation. Modulates also the expression of cellular genes leading to the deregulation of T-cell proliferation, perturbing the integrity of cell cycle checkpoints, the DNA damage response and apopototic pathways. Acts as an ubiquitin E3 ligase and stimulates host IKK complex by catalyzing the assembly of free mixed-linkage polyubiquitin chains, resulting in constitutive activation of the transcription factor NF-kappa-B. Inhibits the host nonsense-mediated mRNA decay (NMD), a cellular process that can actively degrade mRNAs by interacting with host UPF1.