Abstract

The structure of the Escherichia coli ribosomal protein L25 has been determined to an r.m.s. displacement of backbone heavy atoms of 0.62 0.14 Å by multi-dimensional heteronuclear NMR spectroscopy on protein samples uniformly labeled with ¹⁵N or ¹⁵N/¹³C. L25 shows a new topology for RNA-binding proteins consisting of a six-stranded -barrel and two -helices. A putative RNA-binding surface for L25 has been obtained by comparison of backbone ¹⁵N chemical shifts for L25 with and without a bound cognate RNA containing the eubacterial E-loop that is the site for binding of L25 to 5S ribosomal RNA. Sequence comparisons with related proteins, including the general stress protein, CTC, show that the residues involved in RNA binding are highly conserved, thereby providing further confirmation of the binding surface. Tertiary structure comparisons indicate that the six-stranded -barrels of L25 and of the tRNA anticodon-binding domain of glutaminyl-tRNA synthetase are similar.