TAT - Transactivating regulatory protein

HIV TAT acts as transcriptional regulator of viral gene expression by binding to the transactivating responsive sequence (TAR) RNA element.

Homology Model of HIV Tat showing basic domain (blue sidechains) - produced using SwissModel/SPDBV/POVray

Key web links:
ViralZone: HIV-1, HIV replication cycle, HIV resource
PDB: 1MNB (BIV Tat with TAR)
UniProt: P04608 (HIV-1 HXB2 TAT)
Chime Tutorial:  not available
HIV-1/Human Protein Interaction DB: HIV-1 Tat
Los Alamos HIV structure DB:  not available
NCBI: K03455 [EMBL/GenBank/DDBJ]


  • p14 (72 amino acids) - early fully spliced mRNA
  • p16 (86 amino acids) - late incompletely spliced mRNA


  • Regulatory protein.
  • Binds to transactivating responsive sequence (TAR) RNA element and recruits the cyclin T1-CDK9 complex that will in turn hyperphosphorylate the RNA polymerase II. This will promote the elongation phase of HIV-1 transcription from the LTR promoter, allowing full-length transcripts to be produced .
  • TAT also recruits the histone acetyltransferases (HATs) CREBBP, EP300 and PCAF to the chromatin to provide a favorable environment for viral transcription.
  • When provirus emerge from latency, the initial rounds of transcription are very limited until new TAT synthesis occurs after about 2 hours .


  • Cell nucleolus/nucleus
  • Extracellular
  • Host cytoplasm

Additional Information:

  • Early timing of expression.
  • The TAR RNA element forms a hairpin stem-loop structure with a side bulge; the bulge is necessary for Tat binding and function.
  • The TAR RNA element is located at the 5'-terminus of the HIV RNA genome.
  • Tat is one of two viral regulatory factors (Rev is the other regulatory factor), and both are necessary for HIV gene expression.
  • In the absence of Tat expression, HIV generates short (less than 100 nucleotides in length) transcripts.
  • Tat may have similarities with prokaryotic anti-termination factors.
  • Extracellular Tat can be taken up by cells in culture .
  • Tat is essential for viral replication and increases the basal activity of LTR, regardless of integration site.
  • Tat acts as a growth factor for Kaposi's Sarcoma (skin cancer) cells.
  • Tat activates expression of many cellular genes including tumour necrosis factor alpha and transforming growth factor alpha 1 .
  • Tat downregulates expression of some cellular genes by activating expression of bcl-2, and MIP-1 alpha .
  • Stimulation of polymerase elongation results from interactions between Tat and serine kinase CDK9, which phosphorylates the carboxyl-terminal domain of RNA polymerase II .
  • Interactions between Tat and cellular co-factor Cyclin T1 are necessary for recognition of TAR .
  • Additional information about HIV-1 Tat can be found in the BMC Retrovirology review article .

Tat Function & Host-Virus Protein Interactions:[TOP]

Interactions highlighted in the image:

Potential interactions (not in the image):

Genomic Location & Protein Sequence: [TOP]

HIV-1 (HXB2):

          10         20         30         40         50         60         70         80     86
| | | | | | | | |
[download in fasta format]

HIV-1 (Consensus B [Los Alamos HIV database]):

          10         20         30         40         50         60         70          80         90        100 101
| | | | | | | | | | |
[download in fasta format]

Length (HXB2): 86 amino acids
Length (Consensus B): 101 amino acids

Molecular Weight (HXB2): 9837 Da
Molecular Weight (Consensus B): 11525 Da

Theoretical pI (HXB2): 9.88
Theoretical pI (Consensus B): 9.53

Gene Description: Tat consists of spliced exons that are separated by 2334 nucleotides, and they are found on two different reading frames.
The 5' exon is located on the 2nd reading frame (start: 5831 || end: 6045).
The 3' exon is located on the 1st reading frame (start: 8379 || end: 8469).
Tat contains a premature stop codon at position 8424.

Protein Domains/Folds/Motifs: [TOP]

InterPro signature for Immunodeficiency virus transactivating regulatory protein (Tat) - IPR001831

  • translated from mRNA joined from two exons
  • exon 1 (residues 1 - 72) and exon 2 (residues 73 - 101)

Acidic N-terminal Region (residues 1 - 21)
[ more information ]

  • 13 amino acids with amphipathic characteristics

Cysteine Rich Region (residues 22 - 37)
[ more information ]

  • contain 7 cysteines (highly conserved between HIV-1 isolates)
  • individual mutations in 6 of the 7 cysteines abolish Tat function
  • cysteines function in intra-molecular disulfide bond formation in monomeric molecules of Tat (Koken, et al. 1994)

Core Region (residues 38 - 48)
[ more information ]

  • contains RKGLGI motif (conserved between HIV-1, HIV-2 and SIV)

Basic Region (residues 49 - 72)
[ more information ]

  • contains RKKRRQRRR motif
  • confers TAR RNA-Binding activity (specificity of Tat-TAR binding requires additional amino acids outside the basic domain)
  • important for nuclear localization

Cell Adhesion C-terminal Regions (residues 73 - 101)
[ more information ]

  • contains RGD motif (cell adhesion signal for binding to cellular integrins)
  • RGD motif is not found in HIV-2 or SIV Tat proteins
  • contains ESKKKVE motif conserved partially in HIV-2 and SIV (unknown functional significance)

Predicted Motifs: Printer-friendly version

Protein kinase C:
Casein kinase II:
Tyrosine kinase:
cAMP / cGMP kinase:
Cell attachment motif:
Asp Protease motif:
Asp Prot Retro motif:
Arginine-rich Region:
Cysteine-rich Region:
Tryptophan-rich Region:
Zinc-finger CCHC motif:
Leucine Zipper motif:

Secondary Structure prediction:

Antigenic Sites - EMBOSS:

Primary and Secondary Database Entries: [TOP]


ViralZone: HIV-1, HIV replication cycle, HIV resource
PDB/MMDB: Search for HIV-1 & TAT

UniProt: P04608 (HIV-1 HXB2 Tat)
EMBL: K03455; AAB50256.1; [EMBL/GenBank/DDBJ]

AF033819; AAC82591.1; [EMBL/GenBank/DDBJ]

InterPro: IPR001831
Pfam: PF00539
SCOP: none
BLOCKS: P04608
Prosite: P04608
ProtoNet: P04608
Database of Interacting Proteins: P04608
ModBase: P04608
HIV-1/Human Protein Interaction DB: HIV-1 Tat
HIV-1 Sequence Database Los Alamos HIV Sequence Database


Reviews and References: [TOP]

Cite the resource by citing the following paper:
Doherty R et al. BioAfrica's HIV-1 Proteomics Resource: Combining protein data with bioinformatics tools. Retrovirology (2005), 9;2(1):18.

1 - HIV Sequence Compendium 2000
Kuiken CL, Foley B, Hahn B, Korber B, Marx PA, McCutchan F, Mellors JW, Mullins JI, Sodroski J, Wolinksy S.
Theoretical Biol. & Biophys. Group, Los Alamos Nat Lab, LA-UR 01-3860 [Read it online: Compendium]
2 - Retroviruses
Coffin JM, Hughes SH, Varmus HE.
CD-ROM ed. (2002) Cold Spring Harbor Laboratory Press [Read it online: NCBI Bookshelf]
3 - NMR structure of a biologically active peptide containing the RNA-binding domain of
human immunodeficiency virus type I Tat.
Mujeeb A., Peterlin B.M., James T.L., Parslow T.G., Turck C., Bishop K.
PNAS 91: 8248-8252 (1994) [pubmed: 8058789]
4 - Transactivation by HIV-1 Tat via a heterologous RNA-binding protein.
Peterlin B.M., Selby M.J.
Cell 62: 769-776 [pubmed: 2117500]
5 - Minireview - Multifaceted Activities of the HIV-1 Transcriptor of Transcription, Tat
Jeang K.T., Xiao H., Rich E.A.
J Biol Chem 274(41): 28837-28840 [pubmed: 10506122]
6 - Structural and functional characterization of human immunodeficiency virus tat protein.
Ruben S, Perkins A, Purcell R, et al.
J Virol 63: 1-8 (1989) [pubmed: 2535718]
7 - HIV-1 tat trans-activation requires the loop sequence within tar.
Feng S, Holland EC.
Nature 334: 165-167 (1988) [pubmed: 3386755]
8 - A bulge structure in HIV-1 TAR RNA is required for Tat binding and Tat-mediated trans-activation.
Roy S, Delling U, Chen CH.
Genes Dev 4: 1365 (1990) [pubmed: 2227414]
9 - Anti-termination of transcription within the long terminal repeat of HIV-1 by tat gene product.
Kao SY, Calman AF, Luciw PA, Peterlin BM.
Nature 330: 489-493 (1987) [pubmed: 2825027]
10 - The role of Tat in the human immunodeficiency virus life cycle indicates a primary effect on
transcriptional elongation.
Feinberg MB, Baltimore D, Frankel AD.
Proc Natl Acad Sci USA 88: 4045-4049 (1991) [pubmed: 2023953]
11 - Transcription elongation factor P-TEFb is required for HIV-1 tat transactivation in vitro.
Zhu Y, Pe'ery T, Peng J, Ramanathan Y, Marshall N, Marshall T, Amendt B, Mathews MB, Price DH.
Genes Dev. 11: 2622-32 (1997) [pubmed: 9334325]
12 - A novel CDK9-associated C-type cyclin interacts directly with HIV-1 Tat and mediates
its high-affinity, loop-specific binding to TAR RNA.
Wei P, Garber ME, Fang SM, Fischer WH, Jones KA.
Cell. 92: 451-62 (1998) [pubmed: 9491887]
13 - Block of Tat-mediated transactivation of tumor necrosis factor alpha gene expression
by polymeric-TAR decoys.
Brother MB, Chang HK, Lisziewicz J.
Virology 222(1): 252-256 (1996) [pubmed: 8806505]
14 - Human immunodeficiency virus tat gene transfer to the murine central nervous system using a
replication-defective herpes simplex virus vector stimulates transforming growth factor beta 1 gene expression.
Rasty S, Thatikunta P, Gordon J.
Proc Natl Acad Sci USA 93: 6073-6078 (1996) [pubmed: 8650221]
15 - Expression of human immunodeficiency virus type I tat results in down-regulation of bcl-2
and induction of apoptosis in hematopoietic cells.
Sastry KJ, Marin MC, Nehete PN.
Oncogene 13: 487-493 (1996) [pubmed: 8760290]
16 - HIV-1 tat induces the expression of a new hematopoietic cell-specific transcription factor and
downregulates MIP-1 alpha gene expression in activated T cells.
Sharma V, Xu M, Ritter LM.
Biochem Biophys Res Commun 223: 526-533 (1996) [pubmed: 8687429]
17 - HIV-1 gene expression: lessons from provirus and non-integrated DNA
Wu Y.
BMC Retrovirology 1:13 (2004) [pubmed: 15219234 / BMC Retrovirology: 1742-4690-1-13]
18 - Lost in transcription: molecular mechanisms that control HIV latency.
Taube R, Peterlin M.
Viruses 5(3):902-27 (2013) [pubmed: 23518577]
19 - HIV-1 TAR RNA enhances the interaction between Tat and cyclin T1.
Zhang J, Tamilarasu N, Hwang S, Garber ME, Huq I, Jones KA, Rana TM.
J Biol Chem. 275(44):34314-9 (2000) [pubmed: 10944537]
20 - HIV-1 tat transactivator recruits p300 and CREB-binding protein histone acetyltransferases to the viral promoter.
Marzio G, Tyagi M, Gutierrez MI, Giacca M.
Proc Natl Acad Sci U S A 95(23):13519-24 (1998) [pubmed: 9811832]
21 - In vitro and in vivo binding of human immunodeficiency virus type 1 Tat protein and Sp1 transcription factor.
Jeang KT, Chun R, Lin NH, Gatignol A, Glabe CG, Fan H.
J Virol. 67(10):6224-33 (1993) [pubmed: 7690421]
22 - Human DDX3 interacts with the HIV-1 Tat protein to facilitate viral mRNA translation.
Lai MC, Wang SW, Cheng L, Tarn WY, Tsai SJ, Sun HS.
PLoS One 8(7):e68665 (2013) [pubmed: 23840900]
23 - The histone chaperone protein Nucleosome Assembly Protein-1 (hNAP-1) binds HIV-1 Tat and promotes viral transcription.
Vardabasso C, Manganaro L, Lusic M, Marcello A, Giacca M.
Retrovirology 5:8 (2008) [pubmed: 18226242]
24 - HIV-1 tat transactivator recruits p300 and CREB-binding protein histone acetyltransferases to the viral promoter.
Marzio G, Tyagi M, Gutierrez MI, Giacca M.
Proc Natl Acad Sci U S A 95(23):13519-24 (1998) [pubmed: 9811832]
25 - The SWI/SNF chromatin-remodeling complex is a cofactor for Tat transactivation of the HIV promoter.
Mahmoudi T, Parra M, Vries RG, Kauder SE, Verrijzer CP, Ott M, Verdin E.
J Biol Chem. 281(29):19960-8 (2006) [pubmed: 16687403]
26 - Characterization of the influence of mediator complex in HIV-1 transcription.
Ruiz A, Pauls E, Badia R, Riveira-Muñoz E, Clotet B, Ballana E, Esté JA.
J Biol Chem. 289(40):27665-76 (2014) [pubmed: 25100719]
27 - HIV-1 Tat protein-mediated transactivation of the HIV-1 long terminal repeat promoter is potentiated by a novel nuclear Tat-interacting protein of 110 kDa, Tip110.
Liu Y, Li J, Kim BO, Pace BS, He JJ.
J Biol Chem. 277(26):23854-63 (2002) [pubmed: 11959860]
28 - Effect of SWI/SNF chromatin remodeling complex on HIV-1 Tat activated transcription.
Agbottah E, Deng L, Dannenberg LO, Pumfery A, Kashanchi FJ.
Retrovirology 3:48 (2006) [pubmed: 16893449]
29 - The arginine-rich domains present in human immunodeficiency virus type 1 Tat and Rev function as direct importin beta-dependent nuclear localization signals.
Truant R, Cullen BR.
Mol Cell Biol. 19(2):1210-7 (1999) [pubmed: 9891055]
30 - Reciprocal modulatory interaction between human immunodeficiency virus type 1 Tat and transcription factor NFAT1.
Macián F, Rao A.
Mol Cell Biol. 19(5):3645-53 (1999) [pubmed: 10207088]

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