The function of tRNA synthetases is to attach amino acids to tRNAs. 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 synthetases: tRNA synthetases are enzymes responsible for attaching specific amino acids to their corresponding tRNAs. This process is crucial for translation, as the charged tRNA delivers the correct amino acid to the ribosome during protein synthesis.
2. Review the concept of attenuation in the tryptophan operon: Attenuation is a regulatory mechanism in bacteria where transcription of the operon is terminated prematurely based on the availability of tryptophan. When tryptophan levels are high, the ribosome quickly translates the leader peptide, allowing the formation of a terminator structure in the mRNA that halts transcription.
3. Analyze the impact of reduced tRNA synthetase efficiency: If the tRNA synthetase responsible for attaching tryptophan to tRNA functions at only 15% efficiency, fewer tryptophan-charged tRNAs will be available. This would slow down translation of the leader peptide, as the ribosome would stall at tryptophan codons due to the lack of charged tRNAs.
4. Predict the effect on attenuation: The ribosome stalling at tryptophan codons would prevent the formation of the terminator structure in the mRNA. Instead, an anti-terminator structure would form, allowing transcription of the tryptophan operon to continue. This ensures that more tryptophan biosynthetic enzymes are produced to compensate for the reduced efficiency of the tRNA synthetase.
5. Summarize the overall outcome: The mutation in the tRNA synthetase would lead to reduced attenuation of the tryptophan operon, resulting in increased transcription of the operon to produce enzymes for tryptophan synthesis, helping the cell adapt to the lower availability of charged tRNAs.

Key Concepts

tRNA Synthetases

tRNA synthetases are enzymes that catalyze the attachment of specific amino acids to their corresponding tRNA molecules, a process known as aminoacylation. This is crucial for accurate protein synthesis, as each tRNA carries a specific amino acid that corresponds to the codon in the mRNA. A mutation that reduces the efficiency of a tRNA synthetase can lead to a decrease in the availability of the amino acid for protein synthesis, potentially affecting cellular functions.

Attenuation in Gene Regulation

Attenuation is a regulatory mechanism in prokaryotes that controls gene expression, particularly in operons like the tryptophan operon. It involves the formation of specific RNA structures that can either promote or inhibit transcription based on the availability of the amino acid. In the case of tryptophan, if tryptophan levels are low, the ribosome stalls, allowing the formation of a transcriptional antiterminator, leading to continued transcription of the operon.

Impact of Amino Acid Availability

The availability of amino acids directly influences the efficiency of protein synthesis and the regulation of operons. In the scenario of a mutated tRNA synthetase for tryptophan, the reduced efficiency would lead to lower levels of tryptophan in the cell. This could result in altered attenuation of the tryptophan operon, potentially leading to increased transcription of the operon as the cell attempts to compensate for the low tryptophan levels.