Q9 - Start-Codon Selection Mechanisms in Prokaryotic versus Eukaryotic Translation

Both eukaryotes and prokaryotes have a common feature that mRNA starts translation at the AUG codon. Eukaryotic mRNA is usually a monocistron that encodes only one protein, whereas prokaryotic mRNA is often a polycistron that encodes multiple proteins. The following experiments were performed to investigate the mechanism of the AUG codon that initiates translation. Post-translation decomposition need not be considered. (1) For several operons of Escherichia coli, the promoter was replaced with a yeast promoter and introduced into yeast cells. Although all full-length mRNAs were transcribed for all operons, some operons translated only the first gene correctly, while other operons did not translate any genes. (2) The promoters derived from E. coli were ligated to cDNAs obtained by removing introns from several yeast genes and introduced into the E. coli host. Full-length mRNA was transcribed for all operon genes, but there was little translation of any genes. From these experiments, it is considered that the AUG codon that initiates the translation of Escherichia coli and yeast is determined through the following mechanism.

Using the information and data, determine which of the statements are true or which are false.

Question reproduced from IBO 2020, Theoretical Exam 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)