The accuracy of codon recognition by polypeptide release factors

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Messenger RNA (mRNA) contains specific sequences called termination codons that signal the end of protein synthesis.
• Protein release factors (RFs) are crucial for recognizing these stop signals and terminating translation.
• The accuracy of stop codon recognition is vital for preventing errors in protein production.

Purpose of the Study:

• To quantitatively measure the accuracy of termination codon recognition by RF1 and RF2 in Escherichia coli.
• To compare the fidelity of termination codon decoding by RFs with sense codon decoding by transfer RNA (tRNA).
• To investigate the role of RF3 in the termination process.

Main Methods:

• Utilized an in vitro protein synthesis system with purified components from Escherichia coli.
• Measured termination efficiency at stop codons and at sense codons differing by a single mutation.
• Assessed RF1 and RF2 activity in the presence and absence of RF3.

Main Results:

• RF1 and RF2 exhibit high discrimination against sense codons resembling stop codons, ranging from 10^3 to over 10^6 fold.
• This high accuracy is achieved without energy-dependent proofreading mechanisms, unlike tRNA-codon recognition.
• Specific codons (UAU and UGG) were identified as hotspots for premature termination by RFs.

Conclusions:

• Escherichia coli protein release factors demonstrate remarkable precision in recognizing termination codons.
• The fidelity of translation termination is maintained through inherent molecular recognition, not proofreading.
• Understanding these mechanisms provides insights into translational control and potential therapeutic targets.