Final answer:
A transcription factor plays a role in a signal transduction pathway by regulating gene expression.
Step-by-step explanation:
A transcription factor plays a role in a signal transduction pathway by regulating gene expression. Transcription factors are proteins that bind to specific genes on the DNA molecule and either promote or inhibit their transcription. They affect the binding of RNA polymerase to a particular gene, which ultimately controls the production of RNA and proteins.