The nuclear poly(A) binding protein, PABP2, forms an oligomeric particle covering the length of the poly(A) tail

• Published in: Journal of molecular biology 2000-03, Vol.297 (3), p.569-583
• Main Authors: Keller, Rebecca W., Kühn, Uwe, Aragón, Mateo, Bornikova, Larissa, Wahle, Elmar, Bear, David G.
• Format: Article
• Language: English
• Subjects: Allosteric Regulation; Animals; Binding, Competitive; Biopolymers - chemistry; Biopolymers - metabolism; Cattle; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - metabolism; DNA-Binding Proteins - ultrastructure; Hydrogen-Ion Concentration; Microscopy, Atomic Force; Microscopy, Electron; Molecular Weight; mRNA processing; Osmolar Concentration; PABP2 protein; Poly A - chemical synthesis; Poly A - chemistry; Poly A - genetics; Poly A - metabolism; poly(A)-binding protein; Poly(A)-Binding Protein II; Poly(A)-Binding Proteins; polyadenylation; Protein Binding; ribonucleoproteins; RNA - chemistry; RNA - genetics; RNA - metabolism; RNA - ultrastructure; RNA-Binding Proteins - chemistry; RNA-Binding Proteins - metabolism; RNA-Binding Proteins - ultrastructure; Thermodynamics
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1006/jmbi.2000.3572

The mammalian nuclear poly(A) binding protein, PABP2, controls the length of the newly synthesized poly(A) tail on messenger RNAs. To gain a better understanding of the mechanism of length control, we have investigated the structure of the PABP2·poly(A) complex. Electron microscopy and scanning force microscopy studies reveal that PABP2, when bound to poly(A), forms both linear filaments and discrete-sized, compact, oligomeric particles. The maximum diameter of the filament is 7 nm; the maximum diameter of the particle is 21(±2) nm. Maximum particle size is realized when the PABP2·poly(A) complex is formed with poly(A) molecules 200–300 nt long, which corresponds to the average length of the newly synthesized poly(A) tail in vitro and in vivo. The equilibrium between filaments and particles is highly sensitive to ionic strength; filaments are favored at low ionic strength, while particles predominate at moderate to high ionic strength. Nitrocellulose filter binding and gel mobility shift assays indicate that the PABP2·poly(A) particle formed on A 300 is not significantly more stable than complexes formed with smaller species of poly(A). These results are discussed in the context of the proposed functions for PABP2.