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Polyomavirus T-ag binds symmetrical repeats at the viral origin in an asymmetrical mannerPolyomavirus T-ag binds symmetrical repeats at the viral origin in an asymmetrical manner
Structural highlights
FunctionLT_POVBG Isoform large T antigen is a key early protein essential for both driving viral replication and inducing cellular transformation. Plays a role in viral genome replication by driving entry of quiescent cells into the cell cycle and by autoregulating the synthesis of viral early mRNA. Displays highly oncogenic activities by corrupting the host cellular checkpoint mechanisms that guard cell division and the transcription, replication, and repair of DNA. Participates in the modulation of cellular gene expression preceeding viral DNA replication. This step involves binding to host key cell cycle regulators retinoblastoma protein RB1/pRb and TP53. Induces the disassembly of host E2F1 transcription factors from RB1, thus promoting transcriptional activation of E2F1-regulated S-phase genes. Inhibits host TP53 binding to DNA, abrogating the ability of TP53 to stimulate gene expression. Plays the role of a TFIID-associated factor (TAF) in transcription initiation for all three RNA polymerases, by stabilizing the TBP-TFIIA complex on promoters. Initiates viral DNA replication and unwinding via interactions with the viral origin of replication. Binds two adjacent sites in the SV40 origin. The replication fork movement is facilitated by Large T antigen helicase activity. Activates the transcription of viral late mRNA, through host TBP and TFIIA stabilization. Interferes with histone deacetylation mediated by HDAC1, leading to activation of transcription.[UniProtKB:P03070] Publication Abstract from PubMedPolyomaviruses have repeating sequences at their origin of replication that bind the origin-binding domain of virally-encoded large T-antigen. In murine polyomavirus, the central region of the origin contains four copies (P1-P4) of the sequence G(A/G)GGC. These are arranged as a pair of inverted repeats with a two base pair overlap between the repeats at the center. In contrast to SV40, where the repeats are non-overlapping and all four repeats can be simultaneously occupied, the crystal structure of the four central murine polyomavirus sequence repeats in complex with the polyomavirus origin-binding domain reveals that only three of the four repeats (P1,P2, P4) are occupied. Isothermal titration calorimetry confirms that the stoichiometry is the same in solution as in the crystal structure. Consistent with these results, mutation of the third repeat has little effect on DNA replication in vivo. Thus, the apparent two-fold symmetry within the DNA repeats is not carried over to the protein-DNA complex. Flanking sequences such as the A/T rich region are known to be important for DNA replication. When the orientation of the central region was reversed with respect to these flanking regions, the origin was still able to replicate and the P3 sequence (now located at the P2 position with respect to the flanking regions) was again dispensable. This highlights the critical importance of the precise sequence of the region containing the pentamers in replication. Polyomavirus Large T-antigen Binds Symmetrical Repeats at the Viral Origin in an Asymmetrical Manner.,Harrison C, Jiang T, Banerjee P, Meinke G, D'Abramo CM, Schaffhausen B, Bohm A J Virol. 2013 Oct 9. PMID:24109229[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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