Question

Explain translation initiation steps. Include the following terms in your answer: eIF2-GTP, eIF4E, eIF4G, mRNA, tRNA, small ribosomal subunit, and large ribosomal subunit. (virology)

Answer 1

• The first step in translation initiation is the formation of pre-initiation complex that consists ofS small ribosomal subunit, Met-tRNA^met  eIF-2 and GTP.
• Firstly, this pre-initiation complex will bind at the 5' end of the eukaryotic mRNA, this is a step that requires eIF-4F which is also called as cap binding complex and the eIF-3 will bind.
• As this eIF-4F complex comprises of eIF-4A, eIF-4E and eIF-4G, then eIF-4E will bind to the 5 cap on the mRNA while that eIF-4G will interact with poly (A) binding protein on the poly (A) tail of the mRNA.
• This eIF-4A is an ATP dependent RNA helicase that helps in unwinding the secondary structures of the mRNA and hence helps in preparing it for translation.
• This complex will now move along the mRNA in a 5' to 3' direction to search for AUG initiation code. This process is termed as scanning process.
• There is variation in length in 5' untranslated regions of eukaryotic mRNA and can be several nucleotides long and hence may include secondary structures such as hairpin loops and that is probably removed by that initiation factors of the scanning complex.
• The initiation codon contains a short sequence called Kozak consensus (5'-ACCAUGG-3') and once the complex will be positioned over the initiation codon, then 60S large ribosomal subunit will bind to form 80S ininitiation complex, and this step requires the hydrolysis of GTP and that will lead to the release of several initiation factors.
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