Steroids are known to affect the regulation of gene expression the HIV-1 LTR in transient expression assay systems. A number of binding sites for steroid receptors have been mapped by other investigators, and a GR binding site in the negative regulatory element of the HIV-1 LTR was mapped in the course of this study. In a preliminary experiment, this site along with surrounding sequences was shown to exhibit some biological function. Experiments are currently in progress, using improved controls,to test the function of this site both in an in vitro transcription system,as well as in vivo. The in vitro tests would address the question of what sequence determinants in a binding site are necessary for binding, versus what sequence determinants in a binding site are necessary for transcriptional function. The in vivo studies are aimed at defining the correlation between the known steroid responsiveness of the HIV-1 LTR, to sequences and sequence elements in the LTR, and to the presence and the distribution of steroid receptors in specific human T cell lines. Another aspect of this study is in the correlation of the presence of accepted recognition sequences of the GR DBD to its binding characteristics. Determinants for specific recognition by GR which are distinct from the accepted AGAACA sequence were suggested in the initial study, and could involve cooperativity between adjacent specific and semispecific half-sites, nucleic acid structure-specific determinants, and DNA bending. These are possible areas for additional investigation.
