A eukaryotic protein “X” activates a target gene by increasing its transcription when an inducer is added. The results of the experiments are shown below:

Experiment	Results without inducer	Results with inducer
Immunofluorescence of protein “X”	No colocalization with DAPI	Colocalization with DAPI
Electrophoretic Mobility Shift Assay (EMSA)	No binding to probe derived from the promoter of the target gene	No binding to probe derived from the promoter of the target gene
Chromatin immunoprecipitation of the promoter of the target gene	Low acetylation	High acetylation

Which one of the following options is the correct mechanism of protein X-mediated transcriptional activation of the target gene upon addition of the inducer?

Correct option is B

Correct Answer:
(b) It moves to the nucleus and acts as a coactivator
Explanation:
Upon inducer addition, protein X colocalizes with DAPI, indicating nuclear translocation. However, EMSA shows no direct DNA binding, ruling out a transcription factor role. The increase in histone acetylation at the promoter suggests recruitment of chromatin-modifying activities via protein–protein interactions. Thus, protein X functions as a nuclear coactivator, enhancing transcription indirectly.
Information Booster :
· Coactivators do not bind DNA directly but enhance transcription via protein interactions.
· Histone acetylation correlates with open chromatin and active transcription.
· Nuclear translocation upon induction is a common regulatory strategy.
· DAPI colocalization is a standard marker for nuclear localization.
Additional Information (Incorrect Options):
· (a) Cytoplasmic signalling cannot explain promoter-specific histone acetylation.
· (c) Incorrect because protein X is absent from the nucleus without inducer.
· (d) Contradicted by increased transcription and histone acetylation after induction.