A full-length eukaryotic gene is inserted into a bacterial chromosome. The gene contains a complete promoter sequence and a functional polyadenylation sequence, and it has wild-type nucleotides throughout the transcribed region. However, the gene fails to produce a functional protein. What changes would you recommend to permit expression of this eukaryotic gene in a bacterial cell?

검증된 단계별 안내

Understand the problem: Eukaryotic genes contain introns and exons, while bacterial cells lack the machinery to process introns (splicing). This means the eukaryotic gene cannot be properly expressed in bacteria without modifications.

Step 1: Remove introns from the eukaryotic gene. Use reverse transcription to create complementary DNA (cDNA) from the fully processed mRNA of the eukaryotic gene. cDNA lacks introns and can be directly translated in bacteria.

Step 2: Ensure the bacterial transcription machinery can recognize the promoter. Replace the eukaryotic promoter with a bacterial promoter sequence that is compatible with bacterial RNA polymerase.

Step 3: Modify the polyadenylation sequence. Bacteria do not use polyadenylation for mRNA stability. Remove the polyadenylation sequence and ensure the mRNA has a bacterial-compatible ribosome binding site (Shine-Dalgarno sequence) for translation.

Step 4: Confirm codon compatibility. While the genetic code is largely universal, some codon usage preferences differ between eukaryotes and bacteria. Optimize the codon usage of the gene to match the bacterial host for efficient translation.

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주요 개념

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Promoter Compatibility

In prokaryotes, the promoter region must be recognized by bacterial RNA polymerase for transcription to occur. Eukaryotic promoters often contain specific elements that may not be compatible with bacterial transcription machinery. Therefore, using a bacterial promoter or modifying the eukaryotic promoter to include elements recognized by bacteria is essential for successful gene expression.

Transcription and Translation Differences

Eukaryotic genes typically undergo post-transcriptional modifications, such as splicing and polyadenylation, which are not present in prokaryotes. Bacteria lack the machinery for splicing introns, so inserting a eukaryotic gene directly may lead to non-functional transcripts. To express a eukaryotic gene in bacteria, it is crucial to use a cDNA version of the gene that excludes introns.

Codon Usage Bias

Different organisms have varying preferences for specific codons, known as codon usage bias. Eukaryotic genes may contain codons that are rarely used in bacteria, leading to inefficient translation. To enhance protein production in bacterial cells, it may be necessary to optimize the gene's coding sequence to match the codon preferences of the bacterial host.