The polycistronic mrna of a bacterial cell is treated with GMP, poly-a transfera

Question

The polycistronic mrna of a bacterial cell is treated with GMP, poly-a transferase, and ATP, and then it is injected into the cytoplasm of a Eukaryotic vector. Which of the following would occur? (This question was on my biochem exam 3. I there were A-E options. I only remember the answer that I chose. Please explain in detail what would occur). The answer I chose: Translation cannot occur because eukaryotic cells do not recognize shine dalgarno sequence. I dont know if this is correct or not. I am studying for my biochem final. please help!

Explanation / Answer

Ans:

I agree with your answer. The polycistronic mRNA has not undergone the translation in eukaryotes. In eukaryotes, during transcription, synthesized mRNA undergo the modifications called post-transcriptional modifications. Modifications are 1. 5' Capping 2. Polyadenylation 3. Splicing. These are absent in prokaryotic mRNA.

In present experiment:

1. Bacterial mRNA treated with GMP : This step for 5'cappin. 7methyl guanine added to 5' mRNA. Three enzymes have processed this reaction. The enzymes are RNA triphosphatase, Guanine transferase, and methyltransferase. Here with only GMP is present instead of 7 methylguanine. Without enzyme machinery capping not occurred. Importantly, capping site acts as the Ribosomal binding site to initiate the translation and also increases the stability of mRNA.

2. Due to the addition of ATP and polyA transferase may add poly A at 3' end of mRNA. But poly A mainly involved in the termination of transcription and increasing the stability. Not having the role in the initiation of translation.

Conclusion: In this contest, this prokaryotic mRNA unable to undergo translation in the eukaryotic cytoplasm due to the lack of proper 5' capping to bind the eukaryotic ribosomes (80s) to initiate the translation.

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