![]() Kozak’s rules state that the following consensus sequence must appear around the AUG of vertebrate genes: 5′-gccRccAUGG-3′. According to Kozak’s rules, the nucleotides around the AUG indicate whether it is the correct start codon. Many eukaryotic mRNAs are translated from the first AUG, but this is not always the case. Once at the cap, the initiation complex tracks along the mRNA in the 5′ to 3′ direction, searching for the AUG start codon. A cap-binding protein (CBP) and several other IFs assist the movement of the ribosome to the 5′ cap. Instead of depositing at the Shine-Dalgarno sequence, the eukaryotic initiation complex recognizes the 7-methylguanosine cap at the 5′ end of the mRNA. However, Met-tRNA i is distinct from other Met-tRNAs in that it can bind IFs. The methionine on the charged initiator tRNA, called Met-tRNA i, is not formylated. In eukaryotes, a similar initiation complex forms, comprising mRNA, the 40S small ribosomal subunit, eukaryotic IFs, and nucleoside triphosphates (GTP and ATP). After the formation of the initiation complex, the 30S ribosomal subunit is joined by the 50S subunit to form the translation complex. ![]() When an in-frame AUG is encountered during translation elongation, a non-formylated methionine is inserted by a regular Met-tRNA Met. coli, but it is usually removed after translation is complete. The fMet begins every polypeptide chain synthesized by E. Binding of the fMet-tRNA Metf is mediated by the initiation factor IF-2. The formylation creates a “faux” peptide bond between the formyl carboxyl group and the amino group of the methionine. This tRNA carries the amino acid methionine, which is formylated after its attachment to the tRNA. The initiator tRNA then interacts with the start codon AUG. The small subunit of the ribosome is first to bind to the mRNA template at a specific sequence called the Shine-Dalgarno sequence. (Translation Initiation is used under a Creative Commons Attribution-ShareAlike license. The small subunit of the ribosome binds to the messenger RNA, followed by the initiator tRNA and the large subunit of the ribosome. coli, this complex involves the small 30S ribosome, the mRNA template, three initiation factors (IFs IF-1, IF-2, and IF-3), and a special initiator tRNA, called tRNA Metf. Protein synthesis begins with the formation of an initiation complex. coli, a representative prokaryote, and specify any differences between prokaryotic and eukaryotic translation. Here we’ll explore how translation occurs in E. The process of translation is similar in prokaryotes and eukaryotes. ![]() ![]() 14.3 The Mechanism of Protein Synthesis Protein SynthesisĪs with mRNA synthesis, protein synthesis can be divided into three phases: initiation, elongation, and termination. ![]()
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