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.
The start (AUG) codon of the trpL polypeptide is deleted.

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 and contains a short polypeptide coding sequence. This region plays a critical role in regulating transcription through attenuation, which depends on the coupling of transcription and translation in prokaryotes.
2. Recognize the importance of the start codon (AUG): The start codon is essential for initiating translation of the trpL polypeptide. Without it, the ribosome cannot begin translating the leader peptide, which disrupts the formation of the leader polypeptide.
3. Analyze the impact on ribosome stalling: In normal conditions, the ribosome stalls at the trp codons in the leader sequence when tryptophan levels are low, allowing the formation of an antiterminator structure in the mRNA. If the start codon is deleted, translation of the leader peptide cannot occur, preventing ribosome stalling and disrupting attenuation control.
4. Consider the effect on transcription termination: Without ribosome stalling, the terminator structure (a stem-loop followed by a poly-U sequence) may form regardless of tryptophan levels. This could lead to premature termination of transcription of the trp operon genes, reducing their expression even when tryptophan is scarce.
5. Summarize the likely outcome: The deletion of the start codon in the trpL region would likely impair attenuation control, leading to a loss of proper regulation of the trp operon. This could result in reduced transcription of the operon genes under conditions where tryptophan is needed.

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 (trpL) determines whether transcription continues or is terminated prematurely. This process is sensitive to the levels of tryptophan, allowing the cell to adjust gene expression based on nutrient availability.

trp Operon

The trp operon is a cluster of genes in bacteria that encode enzymes necessary for the biosynthesis of the amino acid tryptophan. It is regulated by both repression and attenuation, allowing the cell to efficiently manage resources and respond to changes in tryptophan levels, ensuring that the synthesis of tryptophan occurs only when needed.

Mutations and Their Effects

Mutations are changes in the DNA sequence that can affect gene function. In the context of the trpL region, a deletion of the start codon (AUG) would prevent the synthesis of the trpL polypeptide, disrupting the formation of the necessary RNA structures for proper attenuation control, potentially leading to continuous transcription of the trp operon regardless of tryptophan levels.