A genetic circuit in HIV that decides whether it switches on or stays dormant could hold the key to anti-HIV therapy, according to a new study. As part of the study, researchers at the University of California have in fact been able to "switch off' the circuit, driving HIV to dormancy. The study has also provided a new tool for probing cellular and viral regulation, and for understanding how stem cells choose between different developmental fates. Findings of the study have been published in the latest issue of the Journal Nature Genetics. A challenge of the work, according to Simpson, is that the process involved in how the switch operates cannot be directly observed. Leor S Weinberger and his colleagues said their study was able to measure the level of "noise', or randomness, in HIV gene expression and use it to probe how HIV decides to replicate or remain dormant. "It's significant for two reasons,' said Weinberger. "First, many researchers are interested in determining which cellular processes generate biological noise. "We, instead, asked if the cellular noise could tell us anything about HIV and the cell