Multifaceted Activities of the HIV-1 Transactivator of Transcription, Tat*

Human immunodeficiency virus, type 1 (HIV-1) is the etiological agent for the acquired immunodeficiency syndrome (AIDS). HIV-1 is a retrovirus that encodes a small nuclear transcriptional activator protein, Tat (Fig. 1). In vivo, Tat is required for virus replication and is conserved in the genomes of all primate lentiviruses (1). Over the past decade, the transcriptional function(s) of Tat (reviewed in detail several years ago (2)) has been intensely investigated. It has become clear that a primary role for Tat is in regulating productive and processive transcription from the HIV-1 long terminal repeat (LTR). Tat also has other activities; some are consistent with that of a secreted growth factor (3–5) and a potentiator of reverse transcription (6). Here we review recent insights into the multifaceted activities of Tat.