Question

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

Short answer

Answer: The sigma factor plays a crucial role in bacterial RNA polymerase by helping the core enzyme recognize specific DNA sequences known as promoters, where transcription should begin. It guides the RNA polymerase to the correct initiation site, facilitating the accurate start of the transcription process. After transcription has initiated, the sigma factor dissociates from the core enzyme.

Step-by-step solution

Introduction to RNA Polymerase

RNA polymerase is an essential enzyme in bacteria responsible for the synthesis of RNA from a DNA template through a process called transcription. It consists of multiple subunits, which combine to form functional complexes. Understanding the structure of RNA polymerase and the function of its components is crucial in explaining its role in bacterial protein synthesis.

The Structure of Bacterial RNA Polymerase

In bacteria, RNA polymerase is composed of multiple subunits, typically five: two alpha (\(\alpha\)) subunits, a beta (\(\beta\)) subunit, a beta prime (\(\beta'\)) subunit, and an omega (\(\omega\)) subunit. These subunits come together to form a complex structure responsible for binding to the DNA template and catalyzing the formation of RNA molecules.

The Core Enzyme

The core enzyme of bacterial RNA polymerase consists of the aforementioned subunits: two \(\alpha\) subunits, one \(\beta\) subunit, one \(\beta'\) subunit, and one \(\omega\) subunit. The core enzyme alone has the ability to synthesize RNA, but it cannot specifically recognize promoter sequences in the DNA template, which is required to initiate transcription accurately.

The Sigma Factor

The sigma (\(\sigma\)) factor is a protein that binds to the core enzyme and helps it recognize the specific DNA sequences called promoters, where transcription should begin. The sigma factor's primary role is to guide the RNA polymerase to the correct initiation site and facilitate the precise start of transcription. The combined structure of the core enzyme and the sigma factor is known as the RNA polymerase holoenzyme. Once the transcription process starts, the sigma factor dissociates from the core enzyme, allowing the latter to continue synthesizing RNA without the help of the sigma factor.