Site specific system for generating diversity protein sequences

1. A single recombinant nucleic acid molecule or pair of recombinant nucleic acid molecules comprising

a variable region (VR) operably linked to a donor template region (TR)

wherein said TR comprises an imperfect repeat of the sequence in said VR due to the substitution of non-adenine nucleotides in VR at positions corresponding to one or more adenine nucleotides in TR and said TR is operably linked to a reverse transcriptase (RT) coding sequence which said RT directs at sites of adenine in said TR site-specific mutagenesis of said VR, and

wherein the TR and RT coding sequence are heterologous to each other.

2. The molecule of claim 1 , wherein said VR is all or part of a sequence encoding a specific binding partner of a target molecule.

3. The molecule of claim 2 , further comprising all of the sequence encoding said binding partner, wherein said VR is optionally the 3′ portion of said sequence encoding said binding partner.

4. The molecule of claim 2 , wherein said binding partner binds a cell surface molecule, a hormone, a growth or differentiation factor, a receptor, a ligand of a receptor, a bacterial cell wall molecule, a viral particle, an immunity or immune tolerance factor, or an MHC molecule.

5. The molecule of claim 2 , wherein said binding partner is a bacteriocin.

6. The molecule or pair of molecules of claim 1 , wherein said TR and RT coding sequences are transcribed under the control of a heterologous promoter, such as the fha promoter.

7. A cell containing the molecule or pair of molecules of claim 1 .

8. A plurality or library of nucleic acid molecules according to claim 1 .

9. The plurality or library of claim 8 , wherein the VR has undergone diversification directed by the TR.