Assignment of resonances of exchangeable protons in the NMR spectrum of the complex formed by Escherichia coli ribosomal protein L25 and uniformly nitrogen-15 enriched 5 S RNA fragment.

The downfield proton NMR spectrum of the aqueous nucleoprotein complex formed by Escherichia coli ribosomal protein L25 and uniformly nitrogen-15 enriched 5 S RNA fragment is presented. Many proton resonances show the effects of scalar coupling to nitrogen-15 and these resonances are assigned to nucleic acid imino protons. Selective nitrogen-15 decoupling difference proton spectroscopy revealed nitrogen-15 and proton chemical shift correlations from which the base types of nucleic acid imino proton resonances could be assigned because the nitrogen-15 chemical shifts of nucleic acid guanine and uracil imino nitrogens have separate small ranges for both nucleoproteins and isolated nucleic acids.