In vitro sorting method

1. A method of preparing a gene product, said method comprising:

a) expressing a genetic element of a plurality of genetic elements to produce an expressed product, wherein said plurality of said genetic elements are dispersed in aqueous droplets of an emulsion;

b) separating an aqueous droplet that contains said expressed product from those that do not; and

c) further expressing the genetic element present in said aqueous droplet, thereby producing said gene product.

2. The method of claim 1 , wherein said emulsion is a water-in-oil emulsion.

3. The method of claim 1 , wherein a plurality of droplets comprise a single genetic element.

4. The method of claim 1 , wherein the aqueous phase of said emulsion further comprises a molecule that interacts with a said expressed product to generate a detectable signal.

5. The method of claim 4 , wherein said separating step comprises detection of said detectable signal.

6. The method of claim 4 , wherein said molecule is a substrate of a said expressed product.

7. The method of claim 4 , wherein detection comprises detecting a change in an optical property of a droplet.

8. The method of claim 7 , wherein said optical property is fluorescence.

9. The method of claim 1 , wherein said step of separating comprises fluorescence activated sorting of said droplets.

10. The method of claim 1 , wherein said plurality of genetic elements is a library of genetic elements.

11. The method of claim 1 , wherein said plurality of genetic elements are physically associated with a known ligand, and said step of separating comprises separating a genetic element that encodes a product that binds said ligand from those that do not.

12. The method of claim 11 , wherein said genetic elements each comprise a sequence encoding a peptide or polypeptide tag, and step (b) comprises the steps of:

i) pooling all genetic elements and their products;

ii) performing affinity selection for said tag; and

iii) isolating nucleic acid bound in step (ii) to identify a genetic element encoding a polypeptide that binds said ligand.

13. The method of claim 12 , wherein step (iii) comprises amplifying said nucleic acid bound in step (ii).

14. The method of claim 11 , wherein said plurality of genetic elements is a library of genetic elements.

15. The method of claim 11 , further comprising the steps of iteratively repeating steps (a)-(b).

16. The method of claim 1 , wherein said plurality of genetic elements are physically associated with a substrate for a reaction in which an expressed product participates, wherein a product of said reaction remains physically associated with a genetic element, and said step of separating comprises separating a genetic element that is physically associated with said product of said reaction from those that are not.

17. The method of claim 16 , wherein said separating comprises affinity selection for said product of said reaction.

18. The method of claim 16 , wherein said separating comprises detection of a change in an optical property of said substrate upon conversion to product.

19. The method of claim 16 , wherein said separating comprises fluorescence activated sorting.

20. The method of claim 16 , wherein said separating comprises the steps of:

i) pooling all genetic elements and their products; and

ii) performing affinity selection for said product.

21. The method of claim 20 , further comprising the step, after step (ii), of amplifying said genetic element.

22. The method of claim 16 , further comprising the steps, after step (b) but before step (c), of:

i) preparing an emulsion of said genetic elements separated in step (b);

ii) incubating said emulsion under conditions sufficient to generate a change in a detectable property of a droplet in said emulsion, wherein said change permits the identification of a genetic element encoding an expressed product.

23. The method of claim 16 , wherein said plurality of genetic elements is a library.