The goal of this project is to find RNA molecules that detect hypoxanthine with great sensitivity and specificity. Hypoxanthine is the product of a family of RNA editing enzymes called ADARs. A sensor that can detect hypoxanthine will facilitate the study of the regulation of ADAR activity. There are naturally occurring guanine sensors called guanine riboswitches. We will use in vitro selection to find variants of a guanine riboswitch that can detect hypoxanthine rather than guanine. While performing the selection experiment, we encountered a technical problem. Instead of isolating hypoxanthine sensors, a group of related RNAs that could not detect hypoxanthine dominated the selected RNA pool. Here we report our efforts to separate these aberrant RNAs from the desired RNAs.