An RNA recognition motif in Wilms' tumour protein (WT1) revealed by structural modelling

The Wilms' tumour suppressor gene 1 (WT1) encodes four C2H2 zinc finger- containing proteins critical for normal mammalian urogenital development. Mutations in this gene are observed in the childhood kidney cancer, Wilms' tumour (WT). WT1 can bind specific DNA targets within the promoters of many genes and both transcriptional repression and activation domains have been identified. On this basis, it has been assumed that regulation of transcription is the basis of WT1 tumour suppressor activity. However, subnuclear localization studies have revealed an association between WT1 proteins and 'speckled bodies' within the nucleus. Degradation of nuclear RNA in cells expressing WT1 abolishes this speckled localization and WT1 co- immunoprecipitates with a number of spliceosomal proteins, suggesting that it may also bind to RNA. Using structural rather than sequence comparison, we have now identified an evolutionarily conserved N-terminal RNA recognition motif (RRM) in all known WT1 isoforms similar to that in the constitutive splicing factor U1A. Given the association between WT1 mutations and Wilms' tumours, this study, together with ether recent findings, may suggest a novel tumour suppression mechanism

X-ray Analysis of B2-Crystallin and Evolution of Oligomeric Lens Proteins.

THE β, γ-crystallins form a class of homologous proteins in the eye lens. Each γ-crystallin comprises four topologically equivalent, Greek key motifs; pairs of motifs are organized around a local dyad to give domains and two similar domains are in turn related by a further local dyad1–4. Sequence comparisons and model building predicted that hetero-oligomeric β-crystallins also had internally quadruplicated subunits, but with extensions at the N and C termini, indicating that β, γ-crystallins evolved in two duplication steps from an ancestral protein folded as a Greek key5–7. We report here the X-ray analysis at 2.1 Å resolution of βB2-crystall in homodimer which shows that the connecting peptide is extended and the two domains separated in a way quite unlike γ-crystallin. Domain interactions analogous to those within monomeric γ-crystallin are intermolecular and related by a crystallographic dyad in the βB2-crystallin dimer. This shows how oligomers can evolve by conserving an interface rather than connectivity. A further interaction between dimers suggests a model for more complex aggregates of β-crystallin in the len