What is the role of transcription factors?

Transcription factors play a crucial role in the regulation of gene expression by assisting RNA polymerase in initiating transcription. They function by binding to specific DNA sequences, typically located in the promoter region of genes, which facilitates the recruitment and assembly of the RNA polymerase complex at the start site of transcription. This interaction is essential for the proper initiation of mRNA synthesis from the DNA template.

In addition to their role in initiating transcription, transcription factors can also influence the rate of transcription and determine the specificity with which genes are activated or repressed, thereby allowing cells to respond to various signals and environmental conditions. Their ability to modulate transcription makes them vital components in gene expression and regulation.

The other options describe processes that do not directly involve the role of transcription factors in transcription initiation. For instance, modifying the structure of mRNA, splicing introns, and adding a poly-A tail are all processes that occur after transcription has already begun and are not directly linked to the functions of transcription factors.