Patent ID: 7179595

Claim:
A method of identifying a non-single-chain antigen-binding unit that is immunoreactive with a desired antigen in a yeast cell, comprising: (a) recombinantly co-expressing within a population of yeast cells (i) a reporter gene operably linked to a first DNA-binding-protein recognition site (DNA-BPRS); (ii) a first antigen fusion gene encoding the desired antigen fused in-frame with a first DNA-binding moiety which specifically binds to said first DNA-BPRS; (iii) a plurality of expression vectors that encodes a genetically diverse repertoire of non-single-chain antigen-binding units, each antigen-binding unit comprising a variable region of a first antibody chain fused to a first dimerization sequence, and a variable region of a second antibody chain fused to a second dimerization sequence and a gene activation moiety; wherein the variable regions of the first and second antibody chains dimerize through an interaction between the first and second dimerization sequences to form the antigen-binding unit; and (b) detecting expression of said reporter gene, wherein an increase in the expression indicates a specific binding between the antigen-binding unit and the desired antigen, thereby identifying an antigen-binding unit that is immunoreactive with the desired antigen.