Now notice only one of these DNA strands is actually used to synthesize our RNA molecule. So to see what we mean, let's take a look at the following diagram. So we can imagine that our initiation factors, these proteins are moving across our DNA. Eventually they reach our promoter region and then the RNA polymerase joins and it unwinds our double stranded molecule, our double helix and it creates this transcription bubble. And now as our RNA polymerase moves across this upper strand which runs from the three to the five direction it uses this strand to basically synthesize our RNA molecule. So it uses this trend because just like DNA polymerase RNA polymerase can only read our DNA strand beginning at the three N and ending at the five end.