​In the context of gene expression, what is the primary function of the mediator complex in eukaryotes?​

Correct option is B

The correct answer is (b).
The mediator complex in eukaryotic cells plays a crucial role in gene expression by acting as a bridge between transcription factors and RNA polymerase II. The mediator complex does not directly modify DNA or RNA, but it helps to bring together the transcription machinery, enabling RNA polymerase II to initiate transcription effectively. It integrates signals from various transcription factors and coordinates the assembly of the transcriptional machinery at the promoter regions of genes, thereby enhancing or repressing gene expression as needed.
Incorrect options-
Option (a) To modify histones to promote transcription: Histone modification is mainly carried out by histone acetyltransferases (HATs) and histone methyltransferases, not by the mediator complex.
Option (c) To promote helicase activity to unwind DNA during transcription initiation: DNA unwinding is facilitated by helicases like TFIIH, not by the mediator complex.
Option (d) To degrade mRNA after transcription: mRNA degradation is performed by RNA decay pathways involving exosomes and other enzymes, unrelated to the mediator.