Colorimetric and fluorescent proteins

1. A CRBPII polypeptide comprising at least 95% sequence identity to SEQ ID NO: 5, said polypeptide comprising a mutation corresponding to Q108K in SEQ ID NO: 5, said polypeptide capable of transmitting or emitting light when bound to a retinoid or fluorescent dye molecule.

2. The polypeptide of claim 1 , wherein the polypeptide further comprises an N-terminal methionine.

3. The polypeptide of claim 1 , wherein the polypeptide has amino acid sequence substitutions in SEQ ID NO: 5 as set forth in:

SEQ ID NO: 7, wherein the amino acid substitutions are Q108K and K40L;

SEQ ID NO: 8, wherein the amino acid substitutions are Q108K and T51D;

SEQ ID NO: 9, wherein the amino acid substitutions are Q108K, K40L, and Y60W;

SEQ ID NO: 10, wherein the amino acid substitutions are Q108K, K40L, and T51V;

SEQ ID NO: 11, wherein the amino acid substitutions are Q108K, K40L, and R58F:

SEQ ID NO: 12, wherein the amino acid substitutions are Q108K, K40L, and R58Y:

SEQ ID NO: 13, wherein the amino acid substitutions are Q108K, T51V, and R58Y;

SEQ ID NO: 14, wherein the amino acid substitutions are Q108K, K40L, T51V, and R58W;

SEQ ID NO: 15, wherein the amino acid substitutions are Q108K, K40L, T51V, R58W, and T53C;

SEQ ID NO: 16, wherein the amino acid substitutions are Q108K, K40L, T51V, R58W, T53C, and T29L;

SEQ ID NO: 17, wherein the amino acid substitutions are Q108K, K40L, T51V, R58W, T53C, T29L, and Y19W;

SEQ ID NO: 18, wherein the amino acid substitutions are Q108K, K40L, T51V, R58W, T53C, T29L, Y19W, and Q4R;

SEQ ID NO: 20, wherein the amino acid substitutions are Q108K, K40L, T51V, R58W, T53C, T29L, Y19W, and Q4W;

SEQ ID NO: 21, wherein the amino acid substitutions are Q108K, K40L, T51V, R58W, T53C, T29L, Y19W, and Q4N;

SEQ ID NO: 22, wherein the amino acid substitutions are Q108K, K40L, T51V, R58W, T53C, T29L, Y19W, and Q4T;

SEQ ID NO: 23, wherein the amino acid substitutions are Q108K, K40L, T51V, R58W, T53C, T29L, Y19W, and Q4E;

SEQ ID NO: 24, wherein the amino acid substitutions are Q108K, K40L, T51V, R58W, T53C, T29L, Y19W, and Q4H;

SEQ ID NO: 25, wherein the amino acid substitutions are Q108K, K40L, T51V, R58W, T53C, T29L, Y19W, and Q4K;

SEQ ID NO: 26, wherein the amino acid substitutions are Q108K, K40L, T51V, R58W, T53C, T29L, Y19W, and Q4L;

SEQ ID NO: 27, wherein the amino acid substitutions are Q108K, K40L, T51V, R58W, T53C, T29L, Y19W, and Q4F; or

SEQ ID NO: 28, wherein the amino acid substitutions are Q108K, K40L, T51V, R58W, T53C, T29L, Y19W, Q4R, and A33W.

4. A nucleic acid encoding the polypeptide of claim 1 .

5. An expression cassette comprising the nucleic acid of claim 4 .

6. A vector comprising the expression cassette of claim 5 .

7. A hybrid nucleic acid comprising the nucleic acid of claim 4 joined to a fusion partner nucleic acid that encodes a fusion partner polypeptide.

8. An expression cassette comprising the nucleic acid of claim 7 .

9. A vector comprising the expression cassette of claim 8 .

10. A method of observing a target protein in vivo comprising contacting a living cell with a retinoid or dye ligand that binds a modified polypeptide encoded by the isolated nucleic acid of claim 7 , wherein the cell expresses a fusion protein comprising the modified polypeptide fused in frame with the target protein.

11. The method of claim 10 wherein the dye ligand is a compound of formula I:

Ring-Y—CHO

wherein:

Ring is an optionally substituted C5-C14 mono-, di- or tricyclic cycloalkyl, aryl or heterocyclic ring, wherein the heterocyclic ring has at least one nitrogen or oxygen ring atom, and wherein the Ring has 1-3 optional substituents that are selected from the group consisting of alkyl, halogen, alkoxy, amino and sulfhydryl; and

Y is a divalent C2-C12 alkenylene chain that optionally substituted with 1-3 alkyl groups.

12. The method of claim 10 , wherein the retinoid is retinal.

13. A CRABPII polypeptide comprising at least 95% sequence identity to SEQ ID NO: 33, said polypeptide comprising a mutation corresponding to Q118K in SEQ ID NO: 33, said polypeptide capble of-transmiting or emitting light when bound to a retinoid or fluorescent dye molecule.

14. The polypeptide of claim 13 , wherein the polypeptide does not have an N-terminal methionine.

15. The polypeptide of claim 13 , wherein the polypeptide has amino acid sequence substitutions in SEQ ID NO: 33 as set forth in:

SEQ ID NO: 41, wherein the amino acid substitutions are R111K, R132Q, Y134F, T54V, R59W, A32W, M93L, and E73A;

SEQ ID NO: 43, wherein the amino acid substitutions are R111K, R132Q, Y134F, T54V, R59W, and A32W;

SEQ ID NO: 44, wherein the amino acid substitutions are R111K, R132L, Y134F, T54V, R59W, and A32W; and

SEQ ID NO: 45, wherein the amino acid substitutions are R111K, R132L, and Y134F.

16. A nucleic acid encoding the polypeptide of claim 13 .

17. An expression cassette comprising the nucleic acid of claim 16 .

18. A vector comprising the expression cassette of claim 17 .

19. A hybrid nucleic acid comprising the nucleic acid of claim 16 joined to a fusion partner nucleic acid that encodes a fusion partner polypeptide.

20. An expression cassette comprising the nucleic acid of claim 19 .

21. A vector comprising the expression cassette of claim 20 .

22. A method of observing a target protein in vivo comprising contacting a living cell with a retinoid or dye ligand that binds a modified polypeptide encoded by the isolated nucleic acid of claim 19 , wherein the cell expresses a fusion protein comprising the modified polypeptide fused in frame with the target protein.

23. The method of claim 22 , wherein the dye ligand is a compound of Formula I:

Ring-Y—CHO

wherein:

Ring is an optionally substituted C5-C14 mono-, di- or tricyclic cycloalkyl, aryl or heterocyclic ring, wherein the heterocyclic ring has at least one nitrogen or oxygen ring atom, and wherein the Ring has 1-3 optional substituents that are selected from the group consisting of alkyl, halogen, alkoxy, amino and sulfhydryl; and

Y is a divalent C2-C12 alkenylene chain that optionally substituted with 1-3 alkyl groups.

24. The method of claim 22 , wherein the retinoid is retinal.