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8.3.1.1. Initiation
Initiation of protein synthesis requires that an mRNA molecule be selected for translation by a ribosome. Once the mRNA binds to the ribosome, the latter finds the correct reading frame on the mRNA, and translation begins. This process involves tRNA, rRNA, mRNA, and at least 10 eukaryotic initiation factors (eIFs), some of which have multiple (three to eight) subunits. Also involved are GTP, ATP, and amino acids. Initiation can be divided into four steps; (1) Dissociation of the ribosome into its 40S and 60S subunits (2) Binding of a ternary complex consisting of met-tRNA, GTP, and eIF-2 to the 40S ribosome to form a preinitiation complex (3) Binding of mRNA to the 40S preinitiation complex (4) Combination of the 40S initiation complex with the 60S ribosomal subunit to form the 80S initiation complex 1) Dissociation of the ribosome Two initiation factors, eIF-3 and eIF-IA, bind to the 40S subunit. This favors dissociation of the 80S ribosome into its 40S and 60S subunits and prevents ressociation. 2)Formation of the 40S preinitiation complex
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