COOPERATIVE ACTION OF CELLULAR PROTEINS YB-1 AND PUR-ALPHA WITH THE TUMOR-ANTIGEN OF THE HUMAN JC POLYOMAVIRUS DETERMINES THEIR INTERACTIONWITH THE VIRAL LYTIC CONTROL ELEMENT

Human JC polyomavirus (JCV) is the etiologic agent of the neurodegener ative disease progressive multifocal leukoencephalopathy, By using JCV as a model, we investigated the role of the viral early protein tumor antigen (TAg) in the binding of two cellular proteins, Pur alpha and YB-1, to JCV regulatory sequences, Results from band-shift assays with purified YB-1, Pur alpha, and TAg indicated that efficient binding of Pur alpha, a strong activator of early gene transcription, to a singl e-stranded target sequence corresponding to the viral lytic control el ement, is diminished in the presence of the late gene activator YB-1, which recognizes the opposite strand of the Pur alpha binding site. Of particular interest was the ability of Pur alpha and TAg to enhance b inding of YB-1 to DNA molecules without being associated with this com plex, Binding studies using a mutant peptide encompassing the N termin us of YB-1 indicated that the C terminus of YB-1 is important for its DNA binding activity, The ability of Pur alpha and TAg to increase bin ding of YB-1 to DNA is independent of the YB-1 C terminus, Similarly, results from band-shift assays using Pur alpha variants indicated that two distinct regions of this protein contribute either to its ability to bind DNA or to its ability to enhance YB-1 DNA binding activity, B ased on the interaction of Pur alpha, YB-1, and TAg and their binding to DNA, a model is proposed for the role of these proteins in transcri ption of viral early and late genes during the lytic cycle.