Y box-binding protein-1 binds preferentially to single-stranded nucleic acids and exhibits 3 '-> 5 ' exonuclease activity

We have previously shown that Y box-binding protein-1 (YB-1) binds preferen tially to cisplatin-modified Y box sequences. Based on structural and bioch emical data, we predicted that this protein binds single-stranded nucleic a cids. In the present study we confirmed the prediction and also discovered some unexpected functional features of YB-1. We found that the cold shock d omain of the protein is necessary but not sufficient for double-stranded DN A binding while the C-tail domain interacts with both single-stranded DNA a nd RNA independently of the cold shock domain. In an in vitro translation s ystem the C-tail domain of the protein inhibited translation but the cold s hock domain did not. Both in vitro pull-down and in vivo co-immunoprecipita tion assays revealed that YB-1 can form a homodimer. Deletion analysis mapp ed the C-tail domain of the protein as the region of homodimerization, We a lso characterized an intrinsic 3'-->5' DNA exonuclease activity of the prot ein. The region between residues 51 and 205 of its 324-amino acid extent is required for full exonuclease activity. Our findings suggest that YB-1 fun ctions in regulating DNA/RNA transactions and that these actions involve di fferent domains.