Identification and properties of the 38 000-Mr poly(A)-binding protein of non-polysomal messenger ribonucleoproteins of cryptobiotic gastrulae of Artemia salina.

The Mr-38 000 poly(A)-binding protein interacts with synthetic and natural RNA. A sequence-independent stoichiometry of one protein per 8 - 12 nucleotides is measured by filter binding and sucrose gradient centrifugation. Specificity for the poly(A) sequence is demonstrated from poly(A)/RNA mixing experiments. The poly(A)-binding protein has been identified as the helix-destabilizing protein HD40[Marvil, D. K., Nowak, L. and Szer, W. (1980) J. Biol. Chem. 255, 6466 - 6472] and is characterized by the existence of at least seven ionic species with a pI ranging from 9.2 to 6.6. Acidic ionic species are generated by phosphorylation with mRNP-associated protein kinase. Different ionic species are present on free mRNP and ribosomes-mRNP preinitiation complexes. The poly(A)-binding protein affects mRNA translation and (A)4 polyadenylation. The multifunctionality of the protein is discussed.