PROSITE documentation PDOC51341
Zinc finger large T-antigen (T-ag) D1-type profile


The group of polyomaviruses is formed by the homonymous murine virus (Py) as well as other representative members such as the simian virus 40 (SV40) and the human BK and JC viruses [1]. Their large T antigen (T-ag) protein binds to and activates DNA replication from the origine of DNA replication (ori). Insofar as is known, the T-ag binds to the origin first as a monomer to its pentanucleotide recognition element. The monomers are then thought to assemble into hexamers and double hexamers, which constitute the form that is active in initiation of DNA replication. When bound to the ori, T-ag double hexamers encircle DNA [2]. T-ag is a multidomain protein that contains an N-terminal J domain (see <PDOC00553>), a central origin-binding domain (OBD) (see <PDOC51287>), and a C-terminal superfamily 3 helicase domain (see <PDOC51206>) [3]. The helicase domain actually contains three distinct structural domains: D1 (domain 1), D2 and D3 (see <PDB:1N25>). D1 is the Zn domain at the N terminus and contains five α-helices (α1-α5). The Zn atom coordinated by a Zn motif is important in holding α3 (α-helix 3) and α4 together, which in turn provide an anchor for α1 and α2. The beginning of α5 packs with α1 and α2 of D1, but its C terminus extends to α6 of D3. The D2 domain contains three conserved helicase motifs related to SF3 helicases, namely the modified version of Walker A and B motifs and motif C. D2 folds into a core β-sheet consisting of five parallel β-strands sandwiched by α-helices. The third domain, D3, is all α-helical Its seven α-helices originate from both the N-terminal region (α6-α8) and the C terminus (α13-α16), with D2 inserted between [4].

The Zn motif of T-Ag was proposed to form a canonical zinc-finger structure for DNA binding. However, the Zn domain (D1) has a globular fold stabilized by the coordination of a Zn atom through the Zn motif, and no classical zinc-finger structure specialized for DNA binding is present. The Zn motif is not directly involved in binding DNA but is instead important for stabilizing the Zn-domain structure [4].

The profile we developed covers the entire T-ag D1-type zinc finger.

Last update:

November 2007 / First entry.


Technical section

PROSITE method (with tools and information) covered by this documentation:

ZF_LTAG_D1, PS51341; Zinc finger large T-antigen (T-ag) D1-type profile  (MATRIX)


1AuthorsIacoangeli A. Melucci-Vigo G. Risuleo G. Santi E.
TitleRole of mouse polyomavirus late region in the control of viral DNA replication: a review.
SourceBiochimie 77:780-786(1995).
PubMed ID8824775

2AuthorsBochkareva E. Martynowski D. Seitova A. Bochkarev A.
TitleStructure of the origin-binding domain of simian virus 40 large T antigen bound to DNA.
SourceEMBO J. 25:5961-5969(2006).
PubMed ID17139255

3AuthorsMeinke G. Bullock P.A. Bohm A.
TitleCrystal structure of the simian virus 40 large T-antigen origin-binding domain.
SourceJ. Virol. 80:4304-4312(2006).
PubMed ID16611889

4AuthorsLi D. Zhao R. Lilyestrom W. Gai D. Zhang R. DeCaprio J.A. Fanning E. Jochimiak A. Szakonyi G. Chen X.S.
TitleStructure of the replicative helicase of the oncoprotein SV40 large tumour antigen.
SourceNature 423:512-518(2003).
PubMed ID12774115

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