Tat is a transcriptional transactivator produced by the human immunodeficiency virus type 1 (HIV-1) and plays a pivotal role in enhancing expression of the viral genome in the infected cells. Although initial studies have suggested that interaction of Tat with the transactivation responsive element (TAR), located within the LTR, is essential for Tat function, subsequent studies indicated that Tat has the ability to augment transcription of viral and cellular genes by a TAR-independent mechanism. In early studies we demonstrated that HIV-1 Tat stimulates transcription of the transforming growth factor, TGF-1, gene in glial cells. In this study, we have identified a cellular protein that interacts with the Tat-responsive region located between nucleotides -323 to -453 of the regulatory sequence of the TGF-1 promoter. Results from footprinting analysis revealed association of cellular proteins with the 130 nucleotide sequence located in the Tat-responsive region. Analysis of the associated protein by UV-crosslinking suggested the involvement of a protein between 40-45 kDa in size which preferentially interacts with the GC/GA rich sequence of the TGF-1 Tat-responsive sequence in a single-stranded configuration. The ability of the previously identified 40 kDa protein, named Pur ␣ to bind to the GC/GA sequence in the single-stranded configuration, similar to those from TGF-1 promoter prompted us to investigate its binding capacity to the TGF-1 sequence and its transcriptional activity on the TGF-1 promoter. Results from band shift studies indicated the association of the bacterially produced Pur ␣ to the TGF-1 DNA sequences positioned within the Tat-responsive region. Overexpression of Pur ␣ in glial cells constitutively producing Tat augmented transcription of the TGF-1 gene. These results are consistent with previous reports on the cooperative action of Pur ␣ and Tat in modulating other eukaryotic promoters. The importance of these findings with regard to deregulation of other cellular genes by HIV-1 Tat is discussed.