Transcription factors are proteins that play a role in initiating and regulating the transcription of DNA into RNA. They work to control gene expression by binding to DNA at a specific target sequence to either activate or hinder transcription. Activators are transcription factors that activate transcription by making it easier for RNA polymerase to bind to the promoter region of the gene of interest. Repressors are transcription factors that hinder transcription by making it more difficult for RNA polymerase to bind to the promoter or begin transcription. The efficiency of transcription factors depends on their ability to identify their target site quickly and selectively.