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
[animated gif: 320x240 ]
ViralZone:HIV-1
PDB: 1MNB (BIV Tat with TAR)
SwissProt: 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]
BioAfrica: Tat Protein Data Mining Tool


Isoforms:

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

Localization:

  • Cell nucleolus / nucleus
  • Extracellular

Function:

  • Regulatory protein
  • Viral transcriptional transactivator
  • Binds to transactivating responsive sequence (TAR) RNA element for viral transcription initiation and/or elongation from LTR promoter (Ref. #7 & #8)
  • Upregulates expression of all viral genes
  • Promotes the elongation phase of HIV-1 transcription, allowing full-length transcripts to be produced
    (Ref. #9 & #10)
  • Represses cellular promoters

Additional Information:

  • Tat functions early in viral infections
  • 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 (Ref. #10)
  • Tat is essential for viral replication (Ref. #6)
  • Tat 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 (Ref. #13) and transforming growth factor alpha 1 (Ref. #14)
  • Tat downregulates expression of some cellular genes by activating expression of bcl-2, and MIP-1 alpha (Ref. #15 & #16)
  • Stimulation of polymerase elongation results from interactions between Tat and serine kinase CDK9, which phosphorylates the carboxyl-terminal domain of RNA polymerase II (Ref. #11)
  • Interactions between Tat and cellular co-factor Cyclin T are necessary for recognition of TAR (Ref. #12)
  • Additional information about HIV-1 Tat can be found in the recent BMC Retrovirology review article (Ref. #17)

Genomic Location: [TOP]

Reference Sequences:

HIV-1 (HXB2):

          10         20         30         40         50         60         70
| | | | | | |
MEPVDPRLEP WKHPGSQPKT ACTNCYCKKC CFHCQVCFIT KALGISYGRK KRRQRRRAHQ NSQTHQASLS
80 86
| |
KQPTSQPRGD PTGPKE
[download in fasta format]

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

          10         20         30         40         50         60         70
| | | | | | |
MEPVDPRLEP WKHPGSQPKT ACTNCYCKKC CFHCQVCFIT KGLGISYGRK KRRQRRRAPQ DSQTHQVSLS
80 90 100 101
| | | |
KQPASQPRGD PTGPKESKKK VERETETDPV D
[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


N-glycosylation:
N-myristoylation:
Amidation:
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:









Protein-Protein Interactions: [TOP]

NIAID HIV-1/Human Protein Interaction Database HIV-1 Tat Entry

  • Human TFIID interacts with HIV-1 Tat
  • Human Sp1 transcription factor interacts with HIV-1 Tat
  • Human Tip60 (60 kDa Tat interactive protein) interacts in the nucleus
  • Human TAK (Tat-associated kinase) is activated by Tat and phosphorylates RNA polymerase II, stimulating elongation.
  • PKR (double-stranded RNA-activated kinase) phosphorylates two serines and one threonine residues immediately adjacent to the basic region of Tat.
  • Tat actively binds to the cellular co-factor Cyclin T1, which facilitates recognition of the transactivation response element (TAR) RNA. (Ref. #12)
  • Interactions between Tat, Cyclin T1 and the serine kinase CDK9 induce phosphorylation of the carboxyl-terminal domain of RNA polymerase II, which stimulates processive polymerase elongation of HIV-1 RNA (Ref. #11)
  • Tat transactivation activity occurs through p300 and CREB-binding protein (CBP), which have histone acetyltransferase activity.
  • After binding to p300 and CBP, Tat recruits them to integrated viral LTR
  • p300 and CBP acetylate histones, weakening the histone-DNA interactions, relieving the repressive effects of the chromatin scaffold on the LTR


Primary and Secondary Database Entries: [TOP]

Identifiers:

ViralZone: HIV-1
PDB/MMDB: Search for HIV-1 & TAT

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

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

PIR: UNKNOWN
HIV: K03455; TAT$HXB2
InterPro: IPR001831
Pfam: PF00539
Prints: PR00055; HIVTATDOMAIN
ProDom: PD000331 (residues 1 - 38) / PD012533 (residues 18 - 48) / PD049438 (residues 19 - 38)
PD269587 (residues 32 - 48) / PD592377 (residues 32 - 86) / PD012093 (residues 58 - 86)
SCOP: none
BLOCKS: P04608
Prosite: P04608
ProtoNet: P04608
ProtoMap: P04608
PRESAGE: P04608
Database of Interacting Proteins: P04608
ModBase: P04608
Swiss-2DPAGE: 2D gel

BioAfrica Tools:
- Tat Protein Data Mining Tool provides real-time analysis of HIV-1 Tat isolates
- HIV Structure BLAST searches for similar HIV sequences that have known structures
- HIV Proteomics Resource contains protein sequence and structure analysis tools

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]




Page last updated by Tulio de Oliveira.