Leor S. Weinberger, professor of chemistry and biochemistry at UC San Diego, with Michael L. Simpson of Oak Ridge National Laboratory and Roy D. Dar of the University of Tennessee, Knoxville, say that their study shows how a developmental decision between HIV’s two “replication fates” is made. The authors were able to measure the level of “noise” or randomness in HIV gene expression and use this noise to probe how HIV decides to replicate or remain dormant.