NMR signal assignment of the polyuridine tract of the single-stranded RNA complexed with Sxl RBD1-RBD2 by using residue selective [5-(2)H]uridine substitutions

Using [5-(2)H]uridine phosphoramidite, we synthesized a series of 2H-labeled Drosophila Sex-lethal (Sxl) target RNAs, in which all the uridine residues except one were specifically replaced by [5-(2)H]uridine. By observing the H5-H6 cross peaks of RNA in the TOCSY spectra, we unambiguously assigned all the base proton resonances of the target RNA in a Sxl x RNA complex. Furthermore, it was shown that Sxl differently recognizes A and G in a position prior to the polyuridine tract.