Summary: Human immunodeficiency virus type 1 (HIV-1) and HIV-2 encode related transcriptional activators known as Tat-1 and Tat-2, respectively, that are required for efficient viral replication. The Tat proteins have been studied extensively, and it appears that their mechanism of action is unique to the primate immunodeficiency viruses or a few distantly related lentiviruses. Here we describe a collection of 24 wild-type and mutant Tat-1 and Tat-2 proteins that are expressed inEscherichia colias fusions with glutathioneS-transferase (GST). The GST-Tat fusions can be used for biochemical studies after simple purification fromE. colilysates in a single step under nondenaturing conditions. The availability of these GST-Tat fusions should be useful to investigators examining biochemical properties of Tat-1 and Tat-2 proteins.E. colicultures harboring GST-Tat fusions described here are available through the National Institute of Health AIDS Research and Reference Reagent Program.