Recognition of polyadenylate RNA by the poly(A)-binding protein

The cocrystal structure of human poly(A)-binding protein (PABP) has been de termined at 2.6 Angstrom resolution. PABP recognizes the 3' mRNA poly(A) ta il and plays critical roles in eukaryotic translation initiation and mRNA s tabilization/degradation. The minimal PABP used in this study consists of t he N-terminal two RRM-type RNA-binding domains connected by a short linker (RRM1/2). These two RRMs form a continuous RNA-binding trough, lined by an antiparallel beta sheet backed by four alpha helices. The polyadenylate RNA adopts an extended conformation running the length of the molecular trough . Adenine recognition is primarily mediated by contacts with conserved resi dues found in the RNP motifs of the two RRMs. The convex dorsum of RRM1/2 d isplays a phylogenetically conserved hydrophobic/acidic portion, which may interact with translation initiation factors and regulatory proteins.