Section 9.4 describes the function of tRNA synthetases in attaching amino acids to tRNAs (see Figure 9.16). Suppose the tRNA synthetase responsible for attaching tryptophan to tRNA is mutated in a bacterial strain with the result that the tRNA synthetase functions at about 15% of the efficiency of the wild-type tRNA synthetase. How would this mutation affect attenuation of the tryptophan operon? Explain your answer.

Verified step by step guidance

1. Understand the role of tRNA synthetase: tRNA synthetases are enzymes that attach specific amino acids to their corresponding tRNAs. In this case, the enzyme attaches tryptophan to its tRNA.
2. Recognize the impact of reduced efficiency: A mutation causing the tRNA synthetase to function at 15% efficiency means that tryptophan is attached to tRNA at a much slower rate.
3. Consider the tryptophan operon: The tryptophan operon is a group of genes used to synthesize tryptophan. It is regulated by attenuation, which is a mechanism that controls gene expression based on tryptophan levels.
4. Analyze the effect on attenuation: With reduced efficiency of tRNA synthetase, there will be less charged tRNA^Trp available, potentially leading to a perceived low tryptophan level in the cell.
5. Predict the outcome: The low level of charged tRNA^Trp may cause the ribosome to stall at the leader peptide region of the mRNA, preventing the formation of the terminator structure and allowing transcription of the tryptophan operon to continue.

Key Concepts

tRNA Synthetases

tRNA synthetases are enzymes that catalyze the attachment of specific amino acids to their corresponding transfer RNA (tRNA) molecules. This process, known as aminoacylation, is crucial for accurate protein synthesis, as it ensures that the correct amino acid is incorporated into the growing polypeptide chain during translation. A mutation that reduces the efficiency of a tRNA synthetase can lead to a decrease in the availability of the corresponding amino acid for protein synthesis.

Attenuation in the Tryptophan Operon

Attenuation is a regulatory mechanism in bacterial operons, particularly the tryptophan operon, that controls gene expression based on the availability of tryptophan. It involves the formation of specific RNA structures during transcription that can either promote or terminate the synthesis of mRNA, depending on the levels of tryptophan. When tryptophan is abundant, the operon is repressed; when it is scarce, transcription proceeds, allowing for the production of enzymes needed for tryptophan synthesis.

Impact of Mutation on Gene Regulation

A mutation in the tRNA synthetase that reduces its efficiency affects the overall availability of tryptophan for protein synthesis. If tryptophan levels drop due to inefficient amino acid attachment, the attenuation mechanism may be altered, potentially leading to increased expression of the tryptophan operon. This change can disrupt the balance of tryptophan synthesis and utilization, impacting the cell's ability to respond to its metabolic needs effectively.