Question

For expression of eukaryotic gene in a prokaryotic system, which sequence has to be inserted from its first codon?

• A. Kozak sequence
• B. Shine Dalgarno sequence
• C. Enhancers
• D. Silencers

Hint:

• Shine-Dalgarno Sequence (Prokaryotes) Ribosome binding site on mRNA, upstream of start codon. Pairs with 16S rRNA.
• Kozak Sequence (Eukaryotes) Consensus sequence around the start codon (AUG) that enhances translation initiation efficiency. Ribosome binds 5' cap and scans.
• For heterologous gene expression (e.g., eukaryotic gene in prokaryote), appropriate regulatory signals of the host system must be provided.

Answer 1

The Correct Option is B

In the context of expressing a eukaryotic gene in a prokaryotic system, it is important to ensure that the mRNA can be effectively translated by the prokaryotic ribosomes. Prokaryotes, such as bacteria, utilize a specific ribosome binding site on mRNA known as the Shine-Dalgarno sequence. This sequence is crucial for the initiation of translation in prokaryotes.

Here is an explanation of why the Shine-Dalgarno sequence is needed:

1. Ribosome Binding Site: The Shine-Dalgarno sequence is a purine-rich sequence found upstream of the start codon in prokaryotic mRNA. It aligns the mRNA on the ribosome, facilitating proper translation initiation.
2. Complementarity: It is complementary to a sequence on the 16S rRNA component of the 30S small ribosomal subunit. This complementarity allows the ribosome to attach to the mRNA in the correct position, ensuring accurate translation.
3. Translational Initiation: Without this sequence, the ribosomes might not attach to the mRNA correctly, leading to failure in translation initiation. To express a eukaryotic gene in prokaryotes, inserting a Shine-Dalgarno sequence prior to the first codon ensures that the ribosome can initiate translation effectively.

Thus, the correct sequence to be inserted from the first codon for the expression of a eukaryotic gene in a prokaryotic system is the Shine Dalgarno sequence.