The invention provides a kit for producing an oligonucleotide library, the library comprising a plurality of oligonucleotides, each oligonucleotide having at least one predetermined position, a randomisation codon selected from a defined group of codons, the coding within the defined group coding for different amino acids, the kit comprises a plurality of different randomisation oligonucleotides comprising: \n (i) a coding strand, the coding strand comprising a randomisation codon; and \n (ii) a substantially complementary non-coding strand, \n wherein each double stranded randomisation oligonucleotide comprises a nucleotide sequence coding for a restriction endonuclease recognition site capable of being recognised by a restriction endonuclease, the restriction endonuclease capable of cleaving the randomisation oligonucleotide upstream or downstream of the endonuclease recognition site at a predetermined cleavage site to create a blunt ended cut.
Oligonucleotide library encoding randomised peptides