DNase activity of the muSOX variants was performed as described previously [16] . Briefly, muSOX variants were in vitro transcribed with the mMessage mMachine T7 Kit (Ambion) and translated using rabbit reticulocyte lysates (Promega). Translational product was incubated with linear DNA at 37uC for the indicated time period and then the DNA was phenol/chloroform extracted, and resolved by agarose gel electrophoresis. One-sixth each IVT reaction was also separated by SDS-PAGE. The gels were then fixed, dried, and visualized by autoradiography to verify equivalent protein expression.