The present invention relates to a method of identifying binding site domains that retain the capacity of binding to an epitope when positioned C-terminal of at least one further domain in a recombinant bi- or multivalent polypeptide. The present invention further relates to a kit comprising components such as panels of recombinant vectors of bacterial libraries transfected with a panel of recombinant vectors which is useful in carrying out the method of the invention. Furthermore, binding site domains and fusion proteins obtainable by the method of the invention as well as antibody-like molecules comprising such domains and proteins are described. Furthermore, pharmaceutical and diagnostic compositions containing the above-described fusion proteins and polypeptides are provided.
