Positive and negative transcriptional regulation differ in that: positive regulation requires that a promoter be present; a promoter is not necessary in negative regulation. in positive regulation, the absence of a regulatory protein promotes transcription; in negative regulation, the absence of a regulatory protein promotes transcription. None of the other answer options are correct. in positive regulation, the binding of a regulatory protein to the DNA is necessary for transcription to occur; in negative regulation, such binding prevents transcription. in positive regulation, the binding of a regulatory protein to the DNA is necessary for transcription to occur; in negative regulation, no such protein is necessary.