Molecular basis for the distinct cellular functions of the Lsm1–7 and Lsm2–8 complexes

3′-processing of U6 snRNA alters its recognition by S. pombe Lsm2–8. (A) Processing of U6 by Usb1 leaves a 3′ cyclic phosphate group on U6, denoted as “>p.” (B) In vitro fluorescence polarization binding assays show that S. pombe Lsm2–8 preferentially binds RNA that has been processed by Usb1. All binding curves and K_d determinations in this work were performed with a restrained Hill coefficient of 1. For reference, the nonrestrained Hill coefficients, which are close to 1, are shown in the figure.