THE STRUCTURE OF THE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 TAR RNA REVEALS PRINCIPLES OF RNA RECOGNITION BY TAT PROTEIN

The human immunodeficiency virus type-1 (HIV-1) Tat protein stimulates transcriptional elongation. Tat is introduced to the transcription ma chinery by binding to the transactivation response region (TAR) RNA st em-loop encoded by the 5' leader sequence found on all HIV-1 mRNAs. We have used multidimensional heteronuclear NMR to determine the structu re of the TAR RNA in the presence of the ADP-1 polypeptide, a 37-mer t hat carries the minimal RNA recognition region of the Tat protein and closely mimics Tat binding specificity In the presence of a variety of ligands, including ADP-1, related basic peptides and the amino acid d erivative argininamide, the bulge region of TAR undergoes a local conf ormational rearrangement and forms a more stable structure. The struct ure of TAR in the bound form has been determined from over 1000 NMR-de rived constraints. The U23 residue at the 5' end of the bulge is posit ioned near G26 and A27 in the major groove, rather than stacked on A22 as in the free TAR. U23 and G26 are brought into close proximity by c ontacts to the guanidinium group and side-chain amide group of a commo n arginine residue. However, the interaction of this guanidinium group with TAR is not the only source of binding specificity Besides NOEs t o the arginine residue participating in the conformational change, ADP -1 shows additional intermolecular NOEs to TAR, suggesting that there are multiple points of contacts between TAR RNA and residues from the basic and core regions of Tat. These structural results provide import ant clues towards the identification of small molecular mass and/or pe ptidomimetic inhibitors of the essential Tat-TAR interaction. (C) 1995 Academic Press Limited