The purification of poly(a)-containing RNA by affinity chromatography

The vast majority of eukaryotic mRNA molecules contain tracts of poly(adenylic) acid, up to 250 bases in length, at the 3' end. This property is very useful from the point of view of mRNA extraction because it forms the basis of a convenient and simple affinity chromatography procedure (1). Under high salt conditions (0.3-0.5M NaCl or KCl), poly(A) will hybridize to oligo(dT)-cellulose or poly(U)-Sepharose. These commercially available materials consist of polymers of about 10-20 nucleotides, covalently bound to a carbohydrate support, and bind RNA containing a poly(A) tract as short as 20 residues. Ribosomal and transfer RNAs do not possess poly(A) sequences and will not bind (see Note 1).