Prokaryotic mRNA and tRNA 5' Ends Explained

The structure of the 5' end of mature prokaryotic messenger RNA (mRNA) and transfer RNA (tRNA) molecules differs significantly due to their distinct synthesis and processing pathways.

mRNA 5' End Structure

• Prokaryotic mRNA synthesis begins with RNA polymerase initiating transcription.
• The very first nucleotide added during transcription contains its inherent triphosphate group ($\text{pppN-}$).
• This initial triphosphate group is typically not removed during the processing of mature prokaryotic mRNA.
• Therefore, the 5' end of most mature prokaryotic mRNAs carries a triphosphate group.

tRNA 5' End Structure

• Prokaryotic tRNAs are transcribed as larger precursor molecules.
• These precursors undergo significant processing, including cleavage by specific enzymes (RNases).
• Enzymatic cleavage during maturation typically removes nucleotides from the 5' end of the precursor transcript.
• This processing action results in the 5' end of the mature tRNA having a monophosphate group ($\text{p}`).

Conclusion

Based on these processing differences, the 5' end of mature prokaryotic mRNAs has a triphosphate group, while the 5' end of mature prokaryotic tRNAs has a monophosphate group.