Activation of the JC virus Tat-responsive transcriptional control element by association of the Tat protein of human immunodeficiency virus 1 with cellular protein Pur alpha.

JC virus is activated to replicate in glial cells of many AIDS patients with neurological disorders. In human glial cells, the human immunodeficiency virus 1 (HIV-1) Tat protein activates the major late promoter of JC virus through a Tat-responsive DNA element, termed upTAR, which is a recognition site for cellular Pur alpha, a sequence-specific single-stranded DNA binding protein implicated in cell cycle control of DNA replication and transcription. Tat interacts with two leucine-rich repeats in Pur alpha to form a complex that can be immunoprecipitated from cell extracts. Tat enhances the ability of purified glutathione S-transferase-Pur alpha (GST-Pur alpha) to bind the upTAR element. Tat acts synergistically with Pur alpha, in a cell-cycle-dependent manner, to activate transcription at an upTAR element placed upstream of a heterologous promoter. Since Pur alpha is ubiquitously expressed in human cells and since PUR elements are located near many promoters and origins of replication, the Tat-Pur alpha interaction may be implicated in effects of HIV-1 throughout the full range of HIV-1-infected cells.