Large T antigen, polyomavirus, C-terminal (IPR010932)

Short name: Lg_T_Ag_Polyomavir_C

Overlapping homologous superfamilies


Domain relationships



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 [PMID: 8824775]. Their large T antigen (T-ag) protein binds to and activates DNA replication from the origin 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 [PMID: 17139255]. T-ag is a multidomain protein that contains an N-terminal J domain, which mediates protein interactions (see PDOC00553, IPR001623), a central origin-binding domain (OBD), and a C-terminal superfamily 3 helicase domain (see PDOC51206, IPR010932) [PMID: 16611889].

This entry represents the helicase domain of LTag, which assembles into a hexameric structure containing a positively charged central channel that can bind both single- and double-stranded DNA [PMID: 12774115]. ATP binding and hydrolysis trigger large conformational changes which are thought to be coupled to the melting of origin DNA and the unwinding of duplex DNA [PMID: 15454080]. These conformational changes cause the angles and orientations between regions of a monomer to alter, creating what was described as an "iris"-like motion in the hexamer. In addition to this, six beta hairpins on the channel surface move longitudinally along the central channel, possibly serving as a motor for pulling DNA into the LTag double hexamer for unwinding.

GO terms

Biological Process

GO:0006260 DNA replication

Molecular Function

GO:0005524 ATP binding
GO:0003677 DNA binding

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.