Protein/(poly)peptide libraries

A method of preparing a library of nucleic acids, wherein each nucleic acid encodes an immunoglobulin variable domain comprising consensus framework sequences, comprising:

• (a) identifying a plurality of immunoglobulin variable domain amino acid sequences, each comprising four consensus framework regions interspaced by three complementary determining regions CDR1, CDR2, and CDR3, wherein said consensus framework regions have been identified by the following steps:
• (i) aligning a plurality of known human immunoglobulin sequences;
• (ii) identifying the conserved framework regions of said known human immunoglobulin sequences;
• (iii) comparing the amino acids at each corresponding position of said conserved framework regions;
• and
• (iv) deducing consensus framework regions from said comparing in step (a)(iii);
• and
• (b) synthesizing a plurality of nucleic acids encoding said plurality of immunoglobulin variable domain amino acid sequences provided in step (a), wherein each of said nucleic acids comprises DNA cleavage sites at the boundary between each consensus framework region and complementary determining region, and wherein each of said cleavage sites is unique within said nucleic acid but common to all nucleic acid sequences of said library at corresponding positions.