A conserved motif in group IC3 introns is a new class of GNRA receptor

Terminal tetraloops consisting of GNRA sequences are often found in biologi cally active large RNAs. The loops appear to contribute towards the organiz ation of higher order RNA structures by forming specific tertiary interacti ons with their receptors. Group IC3 introns which possess a GAAA loop in th e. L2 region often have a phylogenetically conserved motif in their P8 doma ins. In this report, we show that this, conserved motif stands as a new cla ss of receptor that distinguishes the sequences of GNRA loops less stringen tly than previously known receptors. The motif can functionally substitute an 11 nt motif receptor in the Tetrahymena ribozyme. Its structural and fun ctional similarity to one class of synthetic receptors obtained from in vit ro selection is observed.