Polyoma Large T antigen (PyLT) is a viral oncoprotein that targets cell proteins important for growth regulation. PyLT has two functional domains. Here we report 1H, 15N, 13C backbone and 13C beta assignments of 76% of the residues of the polyomavirus large T antigen N-terminal domain (PyLTNT) that is sufficient to regulate cell phenotype. PyLTNT is substantially unfolded even in regions known to be critical for its biological function. The protein also includes a previously characterised J domain that although conformationally influenced by the residue extension, retains its folded state unlike the majority of the protein sequence.