Final answer:
RNA polymerase, an enzyme essential for transcription, binds to DNA at promoters with the help of the σ factor. It synthesizes RNA from DNA without needing a primer and disengages upon encountering a termination sequence, completing the transcription process.
Step-by-step explanation:
RNA Polymerase and Transcription Initiation
RNA polymerase is an enzyme responsible for transcribing DNA to RNA. It binds to a specific DNA sequence known as the promoter, where transcription is initiated. The σ factor of RNA polymerase is critical for recognizing the promoter and binding DNA to commence transcription.
Transcription begins when the RNA polymerase forms a 'closed complex' with the promoter. The DNA then unwinds to form an 'open complex', allowing the RNA polymerase to begin synthesizing RNA in the 5'→3' direction, without the need for a primer. The core enzyme of RNA polymerase in prokaryotes, such as E. coli, is made up of several subunits (α, α, β, and β'), while the σ subunit is exclusively involved in transcription initiation.
The signal to end transcription, also known as the termination signal, comes from a specific sequence of nucleotides on the DNA template called a stop signal. The RNA polymerase disengages from the DNA when it reaches this sequence, releasing the newly synthesized RNA and allowing the DNA to recoil back into its double helix structure.