Final answer:
A protein that acts at DNA target sites in the genome to regulate gene expression is called a transcription factor. These regulatory proteins, which include activators and repressors, bind to DNA near promoters and are responsive to environmental stimuli.
Step-by-step explanation:
A protein that can diffuse through the cytoplasm and act at DNA target sites elsewhere in the genome is called a transcription factor. These are a type of regulatory protein involved in regulating gene expression. Each body cell, having the entire genome, manages different gene expression through specific transcription factors. These transcription factors bind to DNA at certain regulatory elements which are typically located near promoters. There are two main types of regulatory proteins that function as transcription factors: activators and repressors. Activators promote transcription by enhancing the interaction of RNA polymerase with the promoter, whereas repressors prevent transcription by blocking the progress of RNA polymerase along the DNA strand. Moreover, transcription factors often respond to environmental stimuli which cause them to locate their binding sites on DNA and initiate transcription of the required gene