The LH module has recently been identified in a number of RNA associated proteins including vigilin and FMR1, a protein implicated in the fragile X syndrome. In this work, NMR spectroscopy was used to determine the secondary structure in solution of a KH domain (repeat 5 from vigilin). Almost complete assignments were obtained for the 1 H and 1 5 N resonances using uniform 1 5 N-labeling of the protein combined with homo-nuclear 2D 1 HNMR and 3D 1 5 N correlated 1 H NMR. On the basis of NOE patterns, secondary chemical shifts and amide solvent exposure, the secondary structure consists of an antiparallel three stranded β sheet connected by two helical regions. This domain may also be stabilized by an appended C-terminal helix which is common to many but not all members of the KH family.