Question

....... should enter the cell in the case of activation of reporter gene for two hybrid system.

• A. Bait protein
• B. Prey protein
• C. Both bait and prey protein
• D. Either one of them

Hint:

In a two-hybrid system, the interaction of both bait and prey proteins is required to activate the reporter gene, enabling detection of protein-protein interactions.

Answer 1

The Correct Option is C

In a two-hybrid assay, the bait protein carries a DNA-binding domain and docks on the reporter gene's promoter, while the prey protein carries a transcription-activation domain. Neither domain alone can switch the reporter on: the DNA-binding domain has nothing to recruit the transcription machinery with, and the activation domain has no way to reach the promoter by itself.

Only when bait and prey physically interact are the two domains brought together, reconstituting a working transcription factor that turns the reporter gene on.

So both bait and prey protein must enter the cell for reporter gene activation to occur.

Answer 2

It helps to think of the two-hybrid system as a two-piece switch that only works when both halves are present at once.

1. Bait protein: This is one half of the switch (the "positioning" half, fused to the DNA-binding domain). A half-switch by itself has no way to complete a circuit, so it cannot flip the reporter gene on.
2. Prey protein: This is the other half of the switch (the "activating" half, fused to the activation domain). Without the positioning half already in place on the promoter, this half also cannot flip anything on.
3. Both bait and prey protein: Only when both halves are present, and the two test proteins fused to them interact with each other, does the switch complete and the reporter gene turn on -- this is the entire logic of using the assay to detect a protein-protein interaction.
4. Either one of them: A half-switch (only one of the two pieces) can never complete the circuit no matter which half it is, so this option cannot be correct.

Since the assay is specifically designed so the reporter only lights up when both fusion proteins are present and interacting, that is the condition required.

The correct answer is both bait and prey protein.