““What is that 95 percent? Some is junk—remnants of pseudogenes inactivated by evolution.fn4,3 But buried in that are the keys to the kingdom, the instruction manual for when to transcribe particular genes, the on/off switches for gene transcription. A gene doesn’t “decide” when to be photocopied into RNA, to generate its protein. Instead, before the start of the stretch of DNA coding for that gene is a short stretch called a promoterfn5—the “on” switch. What turns the promoter switch on? Something called a transcription factor (TF) binds to the promoter. This causes the recruitment of enzymes that transcribe the gene into RNA. Meanwhile, other transcription factors deactivate genes.””
