It frequently happens that very well studied systems will turn up surprises when the right question is asked. Last week, Columbia University researchers published results of a new assay approach that apparently rules out an assumption about the mode of action of non-nucleoside reverse transcriptase inhibitors (NNRTIs), which are used to treat HIV.

The researchers reported in the Proceedings of the National Academy of Sciences that NNRTIs enhance dimerization of the two enzyme subunits of reverse transcriptase. Normally the enzyme is active as a dimer, so it was expected that