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

Step 1: Understanding the two-hybrid system.
In the two-hybrid system, the goal is to test for protein-protein interactions. The bait protein is fused to a DNA binding domain, and the prey protein is fused to an activation domain. Both proteins are expressed in the cell to assess if they interact, activating the reporter gene.
Step 2: Analyzing the options.
(1) Bait protein: This alone would not activate the reporter gene. It requires interaction with the prey protein.
(2) Prey protein: This alone would not activate the reporter gene. It needs the bait protein to interact.
(3) Both bait and prey protein: Correct — Both proteins need to be present in the cell to test for interaction, which will activate the reporter gene.
(4) Either one of them: This is incorrect because both proteins need to interact to activate the reporter gene.
Step 3: Conclusion.
The correct answer is (3) Both bait and prey protein, as both are necessary for activating the reporter gene in a two-hybrid system.

Answer 2

The yeast two-hybrid system works by splitting a transcription factor into two separate domains and testing whether two proteins of interest bring those domains back together. Testing each option against that mechanism:

1. Bait protein: The bait protein alone carries only the DNA-binding domain. On its own it can dock onto the promoter of the reporter gene, but a DNA-binding domain with no activation domain nearby cannot recruit the transcription machinery, so no reporter expression occurs from bait alone.
2. Prey protein: The prey protein alone carries only the activation domain. Without being brought physically close to the promoter (which only the bait's DNA-binding domain can dock onto), the activation domain cannot switch the reporter gene on.
3. Both bait and prey protein: When both are present and they physically interact, the DNA-binding domain (on bait) is already sitting on the promoter, and the interaction pulls the activation domain (on prey) into position right next to it, reconstituting a functional transcription factor that turns the reporter gene on.
4. Either one of them: Since neither the DNA-binding domain nor the activation domain alone can activate transcription, having "either one" present is not sufficient -- both pieces must come together for the reporter to switch on.

Reporter gene activation is only possible when the two split halves of the transcription factor are reunited by an interaction between the two fusion proteins.

Therefore, the correct answer is both bait and prey protein.