Random peptide library

A library of recombinant vectors in which each vector encodes one of a plurality of heterofunctional fusion proteins comprising:

• (a) a binding domain encoded by an oligonucleotide comprising unpredictable nucleotides in which the unpredictable nucleotides are arranged in one or more contiguous sequences, wherein the total number of unpredictable nucleotides is greater than or equal to 60 and less than or equal to 600, wherein the unpredictable nucleotides have the potential to encode all 20 naturally occurring amino acids, and wherein the coding strand of the unpredictable nucleotides comprises the formula (NNB).sub.n+m where
• N is A, C, G or T;
• B is G, T or C;
• and
• n and m are integers,
• such that 20.ltoreq.n+m.ltoreq.200;
• wherein the binding domain is encoded by a double stranded oligonucleotide assembled by annealing a first nucleotide sequence of the formula 5' X (NNB).sub.n J Z 3', with a second nucleotide sequence of the formula
• 3'Z'OU(NNV).sub.m Y5'
• at corresponding positions Z and Z',
• where X and Y are restriction enzyme recognition sites, such that X.noteq.Y;
• N is A, C, G or T;
• B is G, T or C;
• V is G, A or C;
• n is an integer, such that 10.ltoreq.n.ltoreq.100;
• m is an integer, such that 10.ltoreq.m.ltoreq.100;
• Z and Z' are each a sequence of 6, 9 or 12 nucleotides, such that Z and Z' are complementary to each other;
• and
• J is A, C, G, T or nothing;
• O is A, C, G, T or nothing;
• and
• U is G, A, C or nothing;
• provided, however, if any one of J, O or U is nothing then J, O and U are all nothing;
• and converting the annealed oligonucleotides to a double stranded oligonucleotide;
• and
• (b) an effector domain encoded by an oligonucleotide sequence encoding a protein or peptide that enhances expression or detection of the binding domain,
• said library being capable of being screened to identify a heterofunctional fusion protein having specificity for a ligand of choice.