What is the likely effect of each of the following mutations of the trpL region on attenuation control of trp operon gene transcription? Explain your reasoning.
Two nucleotides are inserted immediately following the polypeptide start codon.

Verified step by step guidance

1. Understand the role of the trpL region in attenuation control: The trpL region is part of the leader sequence of the trp operon. It contains a short peptide-coding sequence and plays a critical role in regulating transcription through attenuation. Attenuation depends on the formation of specific secondary structures (stem-loops) in the mRNA, which are influenced by ribosome activity during translation of the leader peptide.
2. Analyze the mutation: Two nucleotides are inserted immediately following the start codon of the leader peptide. This insertion could alter the reading frame of the leader peptide coding sequence, potentially leading to a frameshift mutation. A frameshift mutation changes the codons downstream of the insertion, likely resulting in a nonfunctional or truncated leader peptide.
3. Consider the impact on ribosome stalling: Ribosome stalling is essential for attenuation control. If the leader peptide is not translated correctly due to the frameshift mutation, ribosome stalling at the trp codons may not occur. This would disrupt the formation of the stem-loop structures required for attenuation.
4. Evaluate the effect on transcription termination: Without proper ribosome stalling, the attenuation mechanism may fail. This could lead to either continuous transcription of the trp operon genes (if termination is prevented) or premature termination of transcription (if the incorrect stem-loop structures form).
5. Summarize the likely outcome: The insertion of two nucleotides immediately after the start codon likely disrupts the attenuation control mechanism, either by preventing proper regulation of transcription or by altering the balance between termination and continuation of transcription. This would affect the operon's ability to respond to tryptophan levels effectively.

Key Concepts

Attenuation Control

Attenuation control is a regulatory mechanism in prokaryotic gene expression, particularly in the trp operon, where the formation of specific RNA structures in the leader region influences transcription termination. This process allows the cell to respond to the levels of tryptophan, ensuring that genes are expressed only when necessary. The trpL region plays a crucial role in this mechanism by determining whether transcription will continue or terminate prematurely.

Mutations and Their Effects

Mutations are changes in the DNA sequence that can alter gene function and expression. In the context of the trp operon, mutations in the trpL region can affect the formation of RNA secondary structures, which are essential for proper attenuation. The insertion of nucleotides can disrupt the normal sequence, potentially leading to altered transcriptional regulation and affecting the operon's response to tryptophan levels.

RNA Secondary Structures

RNA secondary structures are formed by base pairing within a single RNA molecule, influencing its stability and function. In the trp operon, the formation of specific hairpin structures in the trpL region determines whether transcription will terminate or proceed. The insertion of nucleotides can change the ability of the RNA to fold correctly, impacting the efficiency of attenuation and, consequently, the expression of downstream genes.