Abstract
It has been documented that the activity of a specific promoter can be occluded by the presence of another promoter element upstream. We present evidence for a phenomenon contradictory to that predicted by the promoter occlusion theory. Transcription from the hamster aprt (adenine phosphoribosyltransferase) promoter was augmented instead of repressed in transfected mouse L cells when an upstream Moloney murine sarcoma virus enhancer-promoter element was induced with butyrate. Without an adjacent Moloney murine sarcoma virus element, butyrate could not activate the aprt promoter.