Purification and domain structure of core hnRNP proteins A1 and A2 and their relationship to single-stranded DNA-binding proteins

Abstract

Protein A1 (M(r) ~ 32,000), a major glycine-rich protein of heterogeneous nuclear ribonucleoproteins (hnRNP), was purified to near homogeneity under non-denaturing conditions from HeLa cells. Limited proteolysis of the native protein yields a trypsin-resistant N-terminal nucleic acid-binding domain about 195 amino acids long which has a primary structure nearly identical to that of the 195-amino acid-long single-stranded DNA (ssDNA)-binding protein UP1 (M(r) 22,162) from calf thymus. 45 of the 61 glycine residues of A1 are present in the trypsin-sensitive C-terminal domain of the protein which contains no sequences homologous to UP1. Protein A2, another major glycine-rich core hnRNP protein from HeLa, has a domain structure analogous to A1 and appears to be related to ssDNA-binding proteins UP1-B from calf liver and HDP-1 from mouse myeloma in a way similar to the A1/UP1 relationship. In contrast to ssDNA-binding proteins, A1 binds preferentially to RNA over ssDNA and exhibits no helix-destabilizing activity.