Biophysical studies on the mammalian heterogeneous nuclear ribonucleoprotein, A1, and its component domains

Abstract

Protein Al is one of the core proteins present in eukaryotic ribonucleoprotein particles. Al binds to single-stranded (ss) nucleic acids and plays a role in RNA metabolism. Limited proteolysis generates an N-terminal domain (195 amino acid residues) termed UP1, which binds ssDNA and contains 2 putative nucleic acid binding domains. The glycine-rich C-terminal fragment (124 amino acid residues) modulates Al binding to single-stranded lattices, and may itself bind to ssRNA. Aromatic side chain interactions with nucleic acid bases are postulated to contribute to the free energy of binding of single-stranded DNA-binding (SSB) proteins. UP1 contains 1 Trp and 4 Tyr residues, while the C-terminal fragment contains 8 additional Tyr residues. Modifications of fluorophore quantum yield, emission properties and anisotropy induced by complex formation were investigated to address the occurrence of intercalation of aromatic residues of Al and related systems with the nucleic acid bases. Our results indicate that the tryptophan fluorescence properties of Al and UP1 are unchanged by the interaction of these proteins with nucleic acids, whereas tyrosine fluorescence is affected by complex formation.