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 eight uracil nucleotides immediately following region 4 are 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 plays a critical role in regulating transcription through attenuation. Attenuation is a mechanism where transcription is terminated prematurely based on the availability of tryptophan.
2. Recognize the importance of the uracil-rich sequence following region 4: This sequence forms part of the intrinsic terminator structure (a stem-loop followed by a string of uracil residues). The uracil residues are essential for the termination of transcription because they weaken the RNA-DNA hybrid, allowing RNA polymerase to dissociate.
3. Analyze the effect of deleting the uracil nucleotides: Without the uracil residues, the intrinsic terminator structure cannot function properly. This means that transcription termination at the attenuator site will likely fail, allowing RNA polymerase to continue transcribing the structural genes of the trp operon.
4. Consider the physiological implications: If attenuation fails, the trp operon will be transcribed even when tryptophan levels are high, leading to unnecessary production of enzymes involved in tryptophan synthesis. This disrupts the operon's normal regulatory mechanism.
5. Summarize the reasoning: The deletion of the uracil nucleotides immediately following region 4 likely prevents attenuation, resulting in constitutive transcription of the trp operon regardless of tryptophan availability.

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 determines whether transcription continues or is terminated. This process relies on the interaction between the ribosome and the mRNA, allowing the cell to respond to the levels of tryptophan. When tryptophan is abundant, transcription is terminated early, while low levels allow for full transcription.

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 mechanisms, allowing the cell to efficiently manage tryptophan production based on its availability. The operon includes structural genes and regulatory sequences that respond to tryptophan levels in the environment.

Mutations and Their Effects

Mutations are changes in the DNA sequence that can affect gene function and regulation. In the context of the trpL region, mutations such as the deletion of uracil nucleotides can disrupt the formation of RNA secondary structures necessary for proper attenuation control. This can lead to altered transcription levels of the trp operon, potentially resulting in either overproduction or underproduction of tryptophan depending on how the mutation affects the ribosome's interaction with the mRNA.