OB fold domains

An isolated modified OB-fold domain, obtainable from a naturally occurring OB-fold domain and removed from the naturally occurring protein within which it is contained, wherein:

• (a) at least one amino acid residue located in a β-strand of the OB-fold domain binding face is mutated by substitution as compared to the naturally occurring OB-fold domain amino acid residue, or
• (b) at least one amino acid residue located in a β-strand of the OB-fold domain binding face and at least one amino acid residue located in a strand of the OB-fold domain loop region are mutated by substitution as compared to the naturally occurring OB-fold domain amino acid residues,
• (c) at least one modified amino acid residue in a strand of the OB-fold domain loop region is mutated by substitution as compared to the naturally occurring OB-fold domain amino acid residue,
• wherein said isolated modified OB-fold domain is selected from the group consisting of Pyrobaculum aerophilum Asp tRNA synthase OB-fold domain having between 4 and 17 mutated amino acids and Pyrobaculum aerophilum initiation factor IF-5A OB-fold domain having between 2 and 11 mutated amino acid residues;
• and wherein said modified OB-fold domain is soluble and has altered binding characteristics as compared to the naturally occurring OB-fold domain, and wherein said domain specifically binds to a different binding partner than the naturally occurring OB-fold domain.