To spread between cells in the body and hop from person to person, human immunodeficiency virus (HIV) must copy its genetic material, produce viral proteins, and assemble new virus particles. For this complex process to occur, a viral protein called Tat must bind to a section of the virus’s RNA—the molecules that carry instructions for making new proteins—which is called the HIV trans-activation response element (TAR).
The TAR RNA can assume many different shapes, known as conformations. However, the Tat protein can only bind to one of these conformations, and if TAR is in a conformation that does not bind to Tat, HIV won’t replicate. So, understanding how these molecules interact could help scientists design therapies that block HIV replication.