Final answer:
The stretch of DNA where RNA polymerase binds for transcription is called the promoter, which is crucial for forming the initiation complex and starting the elongation process of mRNA synthesis.
Step-by-step explanation:
The stretch of DNA where RNA polymerase binds to initiate transcription is known as the promoter. During the initiation of transcription, a set of transcription factors and RNA polymerase form what is called the initiation complex at this promoter site. Transcription begins when RNA polymerase binds to the promoter, and then it unwinds the DNA to form a transcription bubble, exposing the template strand for RNA synthesis. As the polymerase tracks along the DNA template strand, it synthesizes mRNA in the 5' to 3' direction and rewinds the DNA behind it. This is a crucial aspect of the second stage, called elongation, as part of the transcription process of converting DNA into mRNA.