Modeling loop structures in proteins and nucleic acids: an RNA stem-loop.

We have used a novel modeling technique, based on combining information from several preexisting structures, to generate a three-dimensional (3D) model for the RNA stem-loop responsible for translational repression of the MS2 RNA bacteriophage replicase. Specific features of the model have been tested experimentally by chemical and enzymatic structural probes; results from these experiments have been used to "improve" the model by fixing initial assumptions. The new model and chemical modification data are in part consistent, and further predictions are being tested. The modeling algorithm has a wide range of potential applications, particularly to loop regions in proteins and nucleic acids.