The Scanning Model for Translation: An Update

The Scanning Model for Translation: An Update

February 1989 | Marilyn Kozak
The scanning model for translation initiation in eukaryotes posits that the 40S ribosomal subunit binds to the 5'-end of mRNA and then scans for the first AUG codon in a favorable context to initiate translation. This model is supported by extensive evidence from both higher eukaryotes and yeast, including the "first-AUG rule" that holds for 90-95% of vertebrate mRNAs. The importance of position and context is demonstrated by various experiments, such as site-directed mutagenesis and the effects of upstream AUG codons. The scanning mechanism is further supported by the inability of eukaryotic ribosomes to bind to circular mRNAs and the requirement for ATP hydrolysis during scanning. The scanning model also explains the regulation of translation initiation by upstream AUG codons and the formation of multifunctional proteins from bifunctional mRNAs. However, there are some exceptions to the first-AUG rule, such as the translation of picornaviruses and some cellular mRNAs, which can initiate at internal sites under specific conditions. The scanning model has implications for understanding gene regulation and the mechanisms of viral and cellular gene expression.The scanning model for translation initiation in eukaryotes posits that the 40S ribosomal subunit binds to the 5'-end of mRNA and then scans for the first AUG codon in a favorable context to initiate translation. This model is supported by extensive evidence from both higher eukaryotes and yeast, including the "first-AUG rule" that holds for 90-95% of vertebrate mRNAs. The importance of position and context is demonstrated by various experiments, such as site-directed mutagenesis and the effects of upstream AUG codons. The scanning mechanism is further supported by the inability of eukaryotic ribosomes to bind to circular mRNAs and the requirement for ATP hydrolysis during scanning. The scanning model also explains the regulation of translation initiation by upstream AUG codons and the formation of multifunctional proteins from bifunctional mRNAs. However, there are some exceptions to the first-AUG rule, such as the translation of picornaviruses and some cellular mRNAs, which can initiate at internal sites under specific conditions. The scanning model has implications for understanding gene regulation and the mechanisms of viral and cellular gene expression.
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