 Since the nucleus is the site of transcription , it also contains a variety of proteins that either directly mediate transcription or are involved in regulating the process . These proteins include helicases , which unwind the double @-@ stranded DNA molecule to facilitate access to it , RNA polymerases , which synthesize the growing RNA molecule , topoisomerases , which change the amount of supercoiling in DNA , helping it wind and unwind , as well as a large variety of transcription factors that regulate expression . 
