Question

What would be the likely effect of a mutation that would prevent \(\sigma\) from dissociating from the RNA polymerase core?

Short answer

The mutation would likely reduce transcription efficiency and gene expression.

Step-by-step solution

Understand the Role of σ Factor

The σ factor is a protein essential for the initiation of transcription in bacteria. It binds to RNA polymerase, allowing it to recognize and bind to the promoter region of DNA to start transcription.

Identify the Dissociation Phase

After initiation of transcription, the σ factor typically dissociates from the RNA polymerase core, allowing the core enzyme to continue elongation of the RNA transcript effectively.

Analyze the Mutation Effect

If a mutation prevents the σ factor from dissociating, RNA polymerase may remain tightly bound to the promoter region or experience hindered movement along the DNA, impairing RNA chain elongation.

Consider Transcriptional Outcomes

With continuous σ factor binding, transcription initiation might occur, but elongation could be compromised, potentially leading to reduced or abnormal RNA production, affecting protein synthesis.

Summarize the Effect

The mutation would likely result in inefficient transcription due to improper progression from initiation to elongation, causing an overall reduction in gene expression.

Key concepts

Sigma Factor

The sigma factor is a key protein in the process of gene expression regulation, especially in bacterial cells. It plays a crucial role during the initiation of transcription. The main job of the sigma factor is to help RNA polymerase locate the promoter region of DNA. Think of it as a guide that ensures RNA polymerase attaches itself to the correct starting point on the DNA strand so transcription can begin.

• It binds specifically to RNA polymerase, forming what is known as the holoenzyme.
• This holoenzyme is then capable of recognizing and binding to specific sequences called promoters.
• Once bound, the sigma factor is responsible for the "melting" of DNA, where the double strands open up for transcription.

However, the sigma factor doesn't stay attached for long. After transcription is initiated, it usually dissociates from RNA polymerase, allowing the process to continue smoothly. When issues arise and the sigma factor remains bound, such as in certain mutations, it can impede the transcription process.

Transcription Initiation

Transcription initiation is the first step in converting genetic information from DNA into RNA. It is tightly regulated and heavily reliant on the presence and function of the sigma factor.
Here’s how the process works in a simple sequence:

• The sigma factor, in partnership with RNA polymerase, identifies and binds to the promoter regions of DNA.
• This binding helps to unwind a section of the DNA, creating a "transcription bubble" where transcription can begin.
• RNA polymerase then starts synthesizing a new strand of RNA using the DNA template strand.

During initiation, accuracy is key. The precise location of where transcription begins is crucial because it ensures that the RNA produced matches the gene it is meant to transcribe. Problems in transcription initiation, such as improper binding due to persistent sigma factor association, can lead to errors in gene expression.

RNA Polymerase

RNA polymerase is an enzyme critical to the transcription process. Its main role is to synthesize RNA from a DNA template.
This enzyme works in the following manner:

• Once the promoter is located with the help of the sigma factor, RNA polymerase catalyzes the assembly of RNA nucleotides into a chain.
• It moves along the DNA, "reading" the template strand and building a complementary RNA strand.
• After initiation, the enzyme proceeds to elongate the RNA chain, efficiently adding nucleotides to the growing RNA strand.

Mutations that prevent the sigma factor from dissociating can negatively affect RNA polymerase's ability to elongate the RNA transcript, as the enzyme might remain locked in place or experience stalling. Efficient functioning of RNA polymerase is thus vital for successful transcription and proper gene expression.