Describe the structure of RNA polymerase in bacteria. What is the core enzyme? What is the role of the \(\sigma\) subunit?

RNA polymerase is a multi-subunit enzyme responsible for transcription in bacteria. It is composed of several subunits, which come together to form a holoenzyme. The primary subunits of bacterial RNA polymerase include: - Two α (alpha) subunits - One β (beta) subunit - One β' (beta prime) subunit - One σ (sigma) subunit Each subunit has a specific function and contributes to the overall activity of the enzyme.

The core enzyme of bacterial RNA polymerase is the functional part of the RNA polymerase for RNA synthesis. It is composed of four different subunits, which include: - Two α (alpha) subunits - One β (beta) subunit - One β' (beta prime) subunit The core enzyme is responsible for the actual process of transcription but lacks specificity for promoter regions on DNA. To initiate transcription with high specificity, it must associate with a σ (sigma) subunit.

The σ (sigma) subunit of bacterial RNA polymerase has a critical role in transcription initiation by facilitating the binding of RNA polymerase to specific promoter sequences on DNA. The σ subunit recognizes and binds to conserved promoter sequences ("-10" and "-35" regions) on DNA, enabling the RNA polymerase to precisely initiate transcription at the correct location. Upon binding to the promoter, the σ subunit aids in the unwinding of the DNA strands and the formation of the open complex, allowing the template strand to be fed into the active site of RNA polymerase. Once the transcription process has started, the σ subunit is often released from the holoenzyme, allowing for the elongation phase to occur by the core enzyme. Overall, the σ subunit plays a crucial role in achieving the specificity and accuracy during transcription initiation, ensuring that the RNA is synthesized from the correct starting point.