PNNL

Abstract

1 Ontario Cancer Institute and Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada M5G 2M9; 2 Banting and Best Department of Medical Research and 3 Department of Molecular and Medical Genetics, University of Toronto, Toronto, Ontario, Canada M5S 1A8; 4 Affinium Pharmaceuticals, Toronto, Ontario, Canada M5J 1V6; 5 Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, Connecticut 06030, USA The PWI motif is a highly conserved domain of unknown function in the SRm160 splicing and 3'-end cleavage-stimulatory factor, as well as in several other known or putative pre-mRNA processing components. We show here that the PWI motif is a new type of RNA/DNA-binding domain that has an equal preference for single- and double-stranded nucleic acids. Deletion of the motif prevents SRm160 from binding RNA and stimulating 3'-end cleavage, and its substitution with a heterologous RNA-binding domain restores these functions. The NMR solution structure of the SRm160-PWI motif reveals a novel, four-helix bundle and represents the first example of an -helical fold that can bind single-stranded (ss)RNA. Structure-guided mutagenesis indicates that the same surface is involved in RNA and DNA binding and requires the cooperative action of a highly conserved, adjacent basic region. Thus, the PWI motif is a novel type of nucleic acid-binding domain that likely has multiple important functions in pre-mRNA processing, including SRm160-dependent stimulation of 3'-end formation.