A9Y0B2 · A9Y0B2_9HIV1

Function

function

Extracellular circulating Tat can be endocytosed by surrounding uninfected cells via the binding to several surface receptors such as CD26, CXCR4, heparan sulfate proteoglycans (HSPG) or LDLR. Neurons are rarely infected, but they internalize Tat via their LDLR. Through its interaction with nuclear HATs, Tat is potentially able to control the acetylation-dependent cellular gene expression. Modulates the expression of many cellular genes involved in cell survival, proliferation or in coding for cytokines or cytokine receptors. Tat plays a role in T-cell and neurons apoptosis. Tat induced neurotoxicity and apoptosis probably contribute to neuroAIDS. Circulating Tat also acts as a chemokine-like and/or growth factor-like molecule that binds to specific receptors on the surface of the cells, affecting many cellular pathways. In the vascular system, Tat binds to ITGAV/ITGB3 and ITGA5/ITGB1 integrins dimers at the surface of endothelial cells and competes with bFGF for heparin-binding sites, leading to an excess of soluble bFGF.
Transcriptional activator that increases RNA Pol II processivity, thereby increasing the level of full-length viral transcripts. Recognizes a hairpin structure at the 5'-LTR of the nascent viral mRNAs referred to as the transactivation responsive RNA element (TAR) and recruits the cyclin T1-CDK9 complex (P-TEFb complex) that will in turn hyperphosphorylate the RNA polymerase II to allow efficient elongation. The CDK9 component of P-TEFb and other Tat-activated kinases hyperphosphorylate the C-terminus of RNA Pol II that becomes stabilized and much more processive. Other factors such as HTATSF1/Tat-SF1, SUPT5H/SPT5, and HTATIP2 are also important for Tat's function. Besides its effect on RNA Pol II processivity, Tat induces chromatin remodeling of proviral genes by recruiting the histone acetyltransferases (HATs) CREBBP, EP300 and PCAF to the chromatin. This also contributes to the increase in proviral transcription rate, especially when the provirus integrates in transcriptionally silent region of the host genome. To ensure maximal activation of the LTR, Tat mediates nuclear translocation of NF-kappa-B by interacting with host RELA. Through its interaction with host TBP, Tat may also modulate transcription initiation. Tat can reactivate a latently infected cell by penetrating in it and transactivating its LTR promoter. In the cytoplasm, Tat is thought to act as a translational activator of HIV-1 mRNAs.

Miscellaneous

HIV-1 lineages are divided in three main groups, M (for Major), O (for Outlier), and N (for New, or Non-M, Non-O). The vast majority of strains found worldwide belong to the group M. Group O seems to be endemic to and largely confined to Cameroon and neighboring countries in West Central Africa, where these viruses represent a small minority of HIV-1 strains. The group N is represented by a limited number of isolates from Cameroonian persons. The group M is further subdivided in 9 clades or subtypes (A to D, F to H, J and K).

Caution

Lacks conserved residue(s) required for the propagation of feature annotation.

Features

Showing features for site, binding site.

TypeIDPosition(s)Description
Site11Essential for Tat translocation through the endosomal membrane
Binding site22Zn2+ 1 (UniProtKB | ChEBI)
Binding site25Zn2+ 2 (UniProtKB | ChEBI)
Binding site27Zn2+ 2 (UniProtKB | ChEBI)
Binding site30Zn2+ 2 (UniProtKB | ChEBI)
Binding site33Zn2+ 1 (UniProtKB | ChEBI)
Binding site34Zn2+ 1 (UniProtKB | ChEBI)
Binding site37Zn2+ 1 (UniProtKB | ChEBI)

GO annotations

AspectTerm
Cellular Componentextracellular region
Cellular Componenthost cell cytoplasm
Cellular Componenthost cell nucleolus
Molecular Functionactinin binding
Molecular Functioncyclin binding
Molecular Functionmetal ion binding
Molecular Functionprotein domain specific binding
Molecular Functionprotein serine/threonine phosphatase inhibitor activity
Molecular FunctionRNA-binding transcription regulator activity
Molecular Functiontrans-activation response element binding
Biological Processapoptotic process
Biological ProcessDNA-templated transcription
Biological Processmodulation by virus of host chromatin organization
Biological Processnegative regulation of peptidyl-threonine phosphorylation
Biological Processpositive regulation of transcription elongation by RNA polymerase II
Biological Processpositive regulation of viral transcription
Biological Processsymbiont-mediated suppression of host innate immune response
Biological Processsymbiont-mediated suppression of host translation initiation
Biological Processsymbiont-mediated suppression of host type I interferon-mediated signaling pathway
Biological Processvirus-mediated perturbation of host defense response

Keywords

Names & Taxonomy

Protein names

  • Recommended name
    Protein Tat
  • Alternative names
    • Transactivating regulatory protein

Gene names

    • Name
      tat

Organism names

Accessions

  • Primary accession
    A9Y0B2

Proteomes

Subcellular Location

Host nucleus, host nucleolus
Host cytoplasm
Secreted
Note: Probably localizes to both nuclear and nucleolar compartments. Nuclear localization is mediated through the interaction of the nuclear localization signal with importin KPNB1. Secretion occurs through a Golgi-independent pathway. Tat is released from infected cells to the extracellular space where it remains associated to the cell membrane, or is secreted into the cerebrospinal fluid and sera. Extracellular Tat can be endocytosed by surrounding uninfected cells via binding to several receptors depending on the cell type.

Keywords

PTM/Processing

Features

Showing features for modified residue.

TypeIDPosition(s)Description
Modified residue28N6-acetyllysine; by host PCAF
Modified residue50N6-acetyllysine; by host EP300 and GCN5L2
Modified residue51N6-acetyllysine; by host EP300 and GCN5L2
Modified residue52Asymmetric dimethylarginine; by host PRMT6

Post-translational modification

Acetylation by EP300, CREBBP, GCN5L2/GCN5 and PCAF regulates the transactivation activity of Tat. EP300-mediated acetylation of Lys-50 promotes dissociation of Tat from the TAR RNA through the competitive binding to PCAF's bromodomain. In addition, the non-acetylated Tat's N-terminus can also interact with PCAF. PCAF-mediated acetylation of Lys-28 enhances Tat's binding to CCNT1. Lys-50 is deacetylated by SIRT1.
Asymmetrical arginine methylation by host PRMT6 seems to diminish the transactivation capacity of Tat and affects the interaction with host CCNT1.
Phosphorylated by EIF2AK2 on serine and threonine residues adjacent to the basic region important for TAR RNA binding and function. Phosphorylation of Tat by EIF2AK2 is dependent on the prior activation of EIF2AK2 by dsRNA.
Polyubiquitination by host MDM2 does not target Tat to degradation, but activates its transactivation function and fosters interaction with CCNT1 and TAR RNA.

Keywords

Interaction

Subunit

Interacts with host CCNT1. Associates with the P-TEFb complex composed at least of Tat, P-TEFb (CDK9 and CCNT1), TAR RNA, RNA Pol II. Recruits the HATs CREBBP, TAF1/TFIID, EP300, PCAF and GCN5L2. Interacts with host KAT5/Tip60; this interaction targets the latter to degradation. Interacts with the host deacetylase SIRT1. Interacts with host capping enzyme RNGTT; this interaction stimulates RNGTT. Binds to host KDR, and to the host integrins ITGAV/ITGB3 and ITGA5/ITGB1. Interacts with host KPNB1/importin beta-1 without previous binding to KPNA1/importin alpha-1. Interacts with EIF2AK2. Interacts with host nucleosome assembly protein NAP1L1; this interaction may be required for the transport of Tat within the nucleus, since the two proteins interact at the nuclear rim. Interacts with host C1QBP/SF2P32; this interaction involves lysine-acetylated Tat. Interacts with the host chemokine receptors CCR2, CCR3 and CXCR4. Interacts with host DPP4/CD26; this interaction may trigger an anti-proliferative effect. Interacts with host LDLR. Interacts with the host extracellular matrix metalloproteinase MMP1. Interacts with host PRMT6; this interaction mediates Tat's methylation. Interacts with, and is ubiquitinated by MDM2/Hdm2. Interacts with host PSMC3 and HTATIP2. Interacts with STAB1; this interaction may overcome SATB1-mediated repression of IL2 and IL2RA (interleukin) in T cells by binding to the same domain than HDAC1. Interacts (when acetylated) with human CDK13, thereby increasing HIV-1 mRNA splicing and promoting the production of the doubly spliced HIV-1 protein Nef.Interacts with host TBP; this interaction modulates the activity of transcriptional pre-initiation complex. Interacts with host RELA.

Family & Domains

Features

Showing features for region, motif, compositional bias.

TypeIDPosition(s)Description
Region1-24Interaction with human CREBBP
Region1-48Transactivation
Region22-37Cysteine-rich
Region38-48Core
Region47-101Disordered
Motif49-57Nuclear localization signal, RNA-binding (TAR), and protein transduction
Region49-86Interaction with the host capping enzyme RNGTT
Compositional bias81-101Basic and acidic residues

Domain

The Arg-rich RNA-binding region binds the TAR RNA. This region also mediates the nuclear localization through direct binding to KPNB1 and is involved in Tat's transfer across cell membranes (protein transduction). The same region is required for the interaction with EP300, PCAF, EIF2AK2 and KDR.
The Cys-rich region may bind 2 zinc ions. This region is involved in binding to KAT5.
The cell attachment site mediates the interaction with ITGAV/ITGB3 and ITGA5/ITGB1 integrins, leading to vascular cell migration and invasion. This interaction also provides endothelial cells with the adhesion signal they require to grow in response to mitogens.
The transactivation domain mediates the interaction with CCNT1, GCN5L2, and MDM2.

Sequence similarities

Belongs to the lentiviruses Tat family.

Family and domain databases

Sequence

  • Sequence status
    Complete
  • Length
    101
  • Mass (Da)
    11,613
  • Last updated
    2008-02-05 v1
  • Checksum
    EA9C260526C2CD64
MELVDPNLEPWNHPGSKPTTDCNNCYCKICCWHCQLCFLKKGLGISHGRKKRKHRRGPPQSNKDHQNPIPEQPPSIRRGNPTRPKESKKKVESQTETDPCD

Features

Showing features for compositional bias.

TypeIDPosition(s)Description
Compositional bias81-101Basic and acidic residues

Sequence databases

Nucleotide SequenceProtein SequenceMolecule TypeStatus
EU031914
EMBL· GenBank· DDBJ
ABV91572.1
EMBL· GenBank· DDBJ
Genomic DNA

Similar Proteins

Disclaimer

Any medical or genetic information present in this entry is provided for research, educational and informational purposes only. It is not in any way intended to be used as a substitute for professional medical advice, diagnosis, treatment or care. Our staff consists of biologists and biochemists that are not trained to give medical advice.
We'd like to inform you that we have updated our Privacy Notice to comply with Europe’s new General Data Protection Regulation (GDPR) that applies since 25 May 2018.
FeedbackHelp