Crystals of X29, a Xenopus laevis U8 snoRNA-binding protein with nuclear decapping activity.

Eukaryotic ribosome biosynthesis requires modification (methylation, pseudouridylation) and nucleolytic processing of precursor ribosomal RNAs in the nucleolus. The RNA components of the small nucleolar RNPs (snoRNAs) are essential for many of these events. One snoRNP, called U8, is necessary for maturation of 5.8S and 28S rRNA in vertebrates. In Xenopus laevis, U8 snoRNA was found to bind specifically and with high affinity to a protein called X29. X29 is a Nudix hydrolase, a nucleotide diphosphatase that removes the m(7)G and m(227)G caps from U8 and other RNAs. X29 requires an RNA as substrate and cap analogues are not substrates or inhibitors of cleavage. To study the determinants of X29 activity and its specificity for U8 RNA substrate, X29 was crystallized in an orthorhombic crystal form that diffracts to 2.1 A resolution.