p16 (86 amino acids) - late incompletely spliced mRNA
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
When provirus emerge from latency, the initial rounds of transcription are
very limited until new TAT
synthesis occurs after about 2 hours
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.
can be taken up by cells in culture
Tat is essential for viral
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]
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
Thanks to ViralZone at the Swiss Institute of Bioinformatics (SIB) for allowing the use of their images on bioafrica.net.
Page last updated by Megan Druce, Paula Sommer and Tulio de
Oliveira (UKZN/Africa Centre) & Philippe Le Mercier, Chantal Hulo and Patrick Masson (SIB/ViralZone).