22. A non-enzymatic viral protein X was found to be inducing a cellular gene promoter activity. Although no in vitro DNA binding activity could be identified with X protein, it was found to be co-recruited on the cellular promoter along with a cellular transcription factor in vivo. Which one of the following statements seems to be the best interpretation of the above findings?
(1) X is a DNA-binding protein.
(2) X physically interacts with the transcription factor.
(3) X modifies the chromatin for transcription activation.
(4) X is a chaperone.

Viral Protein X Inducing Cellular Gene Promoter Activity Without Direct DNA Binding

Question Recap:

A non-enzymatic viral protein X induces cellular gene promoter activity but shows no in vitro DNA binding. However, in vivo, it is co-recruited on the promoter along with a cellular transcription factor.

Which statement best explains this?

1. X is a DNA-binding protein.

2. X physically interacts with the transcription factor.

3. X modifies the chromatin for transcription activation.

4. X is a chaperone.

Correct Answer:

(2) X physically interacts with the transcription factor.

Explanation:

• The viral protein X does not bind DNA directly in vitro, ruling out it being a classical DNA-binding protein (eliminating option 1).

• However, X is found co-recruited with a cellular transcription factor on the promoter in vivo, implying it is recruited through protein-protein interactions rather than direct DNA binding. This strongly suggests physical interaction with the transcription factor that binds DNA, helping X to localize to the promoter and activate transcription.

• While viral proteins can modify chromatin (option 3), the question emphasizes co-recruitment with a transcription factor and no direct DNA binding, making protein-protein interaction the primary mechanism here.

• Being a chaperone (option 4) is less likely in this context because the key observation is co-recruitment on the promoter with a transcription factor, which typically involves direct interaction rather than general protein folding assistance.

Supporting Evidence from Literature:

• Viral regulatory proteins often activate transcription without binding DNA directly by interacting with cellular transcription factors or co-activators, modulating the transcription machinery indirectly.

• Examples include adenovirus E1A and herpesvirus VP16 proteins that recruit or stabilize transcription factors or components of the transcription initiation complex without direct DNA binding.

• Such interactions facilitate recruitment of the viral protein to the promoter region, enhancing transcriptional activation.

Summary Table

Conclusion

The best interpretation is that viral protein X physically interacts with the cellular transcription factor, allowing it to be co-recruited to the promoter and induce gene expression without direct DNA binding.