Reporter construct and biosensor for interferon second messenger 2-5A

1. A fusion protein comprising RNase L or a fragment thereof fused to a reporter protein, wherein fragments of the reporter protein are fused to both the N-terminal side and the C-terminal side of the RNase L protein or fragment thereof, and wherein the RNase L or fragment thereof binds to 2′-5′ linked oligoadenylates (2-5A).

2. The fusion protein of claim 1 , wherein the reporter protein is selected from the group consisting of luciferase, green fluorescent protein (GFP), red fluorescent protein (RFP), yellow fluorescent protein (YFP) and sfCHERRY.

3. The fusion protein of claim 1 , wherein the luciferase comprises an N-terminal fragment of luciferase on one side of the RNase L or fragment thereof and a C-terminal fragment of luciferase is fused to the opposite side of the RNase L or fragment thereof from the N-terminal fragment of luciferase.

4. A fusion protein comprising RNase L or a fragment thereof fused to a reporter protein, wherein fragments of the reporter protein are fused to both the N-terminal side and the C-terminal side of the RNase L protein or fragment thereof, wherein the luciferase comprises an N-terminal fragment of luciferase on one side of the RNase L or fragment thereof and a C-terminal fragment of luciferase is fused to the opposite side of the RNase L or fragment thereof from the N-terminal fragment of luciferase, and wherein the luciferase is firefly luciferase and the N-terminal fragment comprises amino acids 1-416 of firefly luciferase and the C-terminal fragment comprises amino acid residues 417-500 of firefly luciferase.

5. A fusion protein comprising RNase L or a fragment thereof fused to a reporter protein, wherein fragments of the reporter protein are fused to both the N-terminal side and the C-terminal side of the RNase L protein or fragment thereof, wherein

i) the reporter protein is GFP and the N-terminal fragment comprises amino acids 1-214 of GFP and the C-terminal fragment comprises amino acid residues 215-230 of GFP; or

ii) the reporter protein is sfCHERRY and the N-terminal fragment comprises amino acids 1-208 of sfCHERRY and the C-terminal fragment comprises amino acid residues 209-226 of sfCHERRY.

6. The fusion protein of claim 1 , wherein the reporter protein is connected to the RNase L or fragment thereof via one or more linkers, optionally wherein the linker comprises a GGGS linker (SEQ ID NO: 1).

7. The fusion protein of claim 1 , wherein the fragment of RNase L comprises all or part of an RNase L ANK domain.

8. The fusion protein of claim 4 , wherein the RNase L or fragment thereof binds to 2′-5′ linked oligoadenylates (2-5A).

9. The fusion protein of claim 1 , further comprising a nuclear localization signal (NLS) or a nuclear export signal (NES).

10. A fusion protein comprising RNase L or a fragment thereof fused to a reporter protein, wherein fragments of the reporter protein are fused to both the N-terminal side and the C-terminal side of the RNase L protein or fragment thereof, wherein binding of RNase L to 2′-5′linked oligoadenylates (2-5A) results in head-to-tail dimerization of the RNase L proteins and activation of the reporter.

11. A nucleotide encoding a fusion protein of claim 1 .

12. A vector expressing the fusion protein of claim 1 .

13. A composition comprising the fusion protein of claim 1 .

14. A method of detecting 2′-5′ linked oligoadenylates (2-5A) comprising contacting a sample with a composition comprising a fusion protein of claim 1 , wherein an increase in reporter signal compared to control is indicative of an increase in 2-5A in the sample.

15. A method of determining levels of double stranded RNA (dsRNA) in a sample comprising contacting the sample with a composition comprising a fusion protein of claim 1 , and detecting levels of dsRNA based on signal emitted from the reporter, wherein an increase in reporter signal compared to control is indicative of an increase in dsRNA in the sample.

16. The method of claim 15 , wherein the increase in dsRNA is associated with an infection or autoimmune disease.

17. A method for detecting or monitoring progression of an immune response in a subject comprising

i) contacting a sample from the subject with a composition comprising a fusion protein of claim 1 ;

ii) detecting levels of intracellular double stranded RNA (dsRNA) based on the signal emitted from the reporter, wherein an increase in dsRNA levels compared to control is indicative of an increasing immune response.

18. A method for treating an immune response in a subject comprising

i) contacting a sample from the subject with a composition comprising a fusion protein of claim 1 ;

ii) detecting levels of intracellular double stranded RNA (dsRNA) based on the signal emitted from the reporter, wherein a change in dsRNA levels compared to control is indicative of a modulated immune response; and,

iii) treating the subject with a therapeutic agent to treat the immune response when there is a change in levels of dsRNA detected.

19. A method for identifying a modulator of 2′-5′ linked oligoadenylate (2-5A) binding to RNase L comprising

i) contacting a sample with a composition comprising a fusion protein of claim 1 in the presence of a candidate modulator compound, and

ii) detecting levels of intracellular double stranded RNA (dsRNA) based on the signal emitted from the reporter after step (i),

wherein when the compound increases 2-5A binding to RNase L and increases dsRNA, the modulator is useful as a cancer therapeutic or anti-viral; or

wherein when the compound decreases 2-5A binding to RNase L and decreases dsRNA, the modulator is useful as a therapeutic to treat autoimmune disease associated with self-dsRNA.

20. A kit comprising a composition comprising a fusion protein comprising RNase L or a fragment thereof fused to a reporter protein, wherein fragments of the reporter protein are fused to both the N-terminal side and the C-terminal side of the RNase L protein or fragment thereof, and instructions for use.