AAV-based conditional expression system

1. A virion comprising a nucleic acid comprising in 5′ to 3′ direction

(i) an adeno-associated virus (AAV) inverted terminal repeat (ITR) sequence;

(ii) at least one AAV promoter which is capable of being activated by at least one helper polypeptide or helper polynucleotide originating or derived from a virus selected from Adenoviridae and Herpesviridae;

(iii) at least one AAV rep gene coding sequence under the control of said promoter of (ii);

(iv) an AAV promoter which is capable of being activated by said at least one helper polypeptide or helper polynucleotide originating from a virus selected from Adenoviridae and Herpesviridae;

(v) a transgenic coding sequence under the control of said promoter of (iv);

(vi) a polyadenylation site; and

(vii) an adeno-associated virus (AAV) inverted terminal repeal (ITR) sequence;

wherein said virion does not comprise an AAV cap gene and/or is not able to express any AAV cap gene products.

2. The virion of claim 1 , wherein said virion comprises AAV capsid proteins.

3. The virion claim 1 , wherein sequences (i) to (vii) are comprised in a single linear nucleic acid.

4. The virion of claim 1 , wherein

(i) the promoter of (ii) is one or more promoters selected from the group consisting of AAV promoters p40, p5, and p19; and

(ii) the promoter of (iv) is full-length p40.

5. The virion of claim 1 , wherein the at least one AAV rep gene coding sequence of (iii) encodes at least one of the AAV Rep78 or the AAV Rep68 polypeptide.

6. A method of determining whether a virus, said virus selected from Adenoviridae and Herpesviridae, is inhibited by an antiviral agent, said method comprising bringing into contact a cell infected with the virion of claim 1 , said infected cell comprising the nucleic acid of the virion of claim 1 , with a sample comprising said virus wherein said contacting is effected (i) in the presence of said antiviral agent and (ii) in its absence, wherein a greater amount of product of the transgenic coding sequence of (v) in case (ii) is indicative of said virus being inhibited by said agent.

7. A method of detecting and/or quantifying infectious virus, said virus selected from Adenoviridae and Herpesviridae, said method comprising bringing into contact a cell infected with the virion of claim 1 , said infected cell comprising the nucleic acid of the virion of claim 1 , with a sample comprising or suspected of comprising said infectious virus, wherein presence and/or amount of product of the transgenic coding sequence of (v) is indicative of the presence and/or the amount of said infectious virus.

8. A method for identifying a compound having antiviral activity against a virus, said virus selected from Adenoviridae and Herpesviridae, said method comprising the steps of:

(a) introducing into cells of a population of cells infected with the virion of claim 1 , said infected cells comprising the nucleic acid of the virion of claim 1 , at least one nucleic acid encoding at least one helper polypeptide originating or derived from a virus selected from Adenoviridae and Herpesviridae;

(b) determining the amount of the product encoded by the transgenic coding sequence of (v) expressed by the cell population of step (a) after said introducing;

(c) contacting a population of cells of step (a) with the compound to be tested;

(d) determining the amount of the product encoded by said transgenic coding sequence of (v) expressed by the cell population of step (c) after said introducing; and

comparing the amount of said product determined in step (b) with the amount of said product determined in step (d), wherein less product determined in step (d), relative to the product determined in step (b) indicates that the tested compound has antiviral activity.

9. The method of claim 8 , further comprising providing in step (a) at least one helper polynucleotide originating or derived from a virus selected from Adenoviridae and Herpesviridae.

10. The method of claim 8 , wherein said introducing comprises infection with a virus selected from Adenoviridae and Herpesviridae.

11. The virion of claim 5 , wherein the at least one AAV rep gene coding sequence of (iii) further encodes at least one of the AAV Rep52 and/or AAV Rep40 polypeptide.

12. The virion of claim 4 , wherein the promoter of (i) is the AAV promoter p5 in combination with the AAV promoter p19.

13. The virion of claim 2 , wherein said virion consists of said AAV capsid proteins and said nucleic acid.