PURIFICATION AND CHARACTERIZATION OF A 70-KILODALTON POLYADENYLATE-BINDING PROTEIN FROM PEA (PISUM-SATIVUM)

A polyadenylate-binding protein (PABP) was purified from cell-free ext racts prepared from pea seedlings (Pisum sativum) by ammonium sulfate precipitation and Affi-Gel Blue and polyadenylate-Sepharose 4B affinit y chromatography. The final preparation from polyadenylate-Sepharose 4 B columns contained a single 70-kilodalton polypeptide with high polya denylate-binding activity. The purified protein was active over a broa d range of ionic strengths and showed temperature and pH optima of 37- degrees-C and pH 6.5, respectively. Specificity studies indicated that the pea PABP was most active with polyadenylic acids, showed some act ivity with polyguanylic acid, and did not bind to polycytidylic acid. Moreover, longer polyadenylate molecules were bound more effectively t han shorter ones. Because these properties are similar to PABPs isolat ed from other sources, we conclude that we have identified, purified, and characterized a plant PABP analogous to those described in yeast a nd animal systems.