eukaryotic 80S initiation complex

Definition

Target type: cellularcomponent

A protein complex composed of the large and small ribosomal subunits, methionyl-initiatior tRNA, and the capped mRNA. The initiator tRNA is positioned at the ribosomal P site at the AUG codon corresponding to the beginning of the coding region. [GOC:hjd, PMID:15145049]

The eukaryotic 80S initiation complex is a multi-component assembly responsible for initiating protein synthesis. It consists of the 40S and 60S ribosomal subunits, mRNA, initiator tRNA (Met-tRNAi), and several initiation factors (eIFs). Here's a breakdown of its cellular components:

**40S Ribosomal Subunit:**
- **Small subunit rRNA (18S rRNA):** Provides the structural framework for the 40S subunit and plays a crucial role in mRNA binding and decoding.
- **40S ribosomal proteins:** Approximately 33 proteins associate with the 18S rRNA to form the functional 40S subunit. These proteins contribute to the subunit's stability, shape, and interaction with other components of the initiation complex.

**60S Ribosomal Subunit:**
- **Large subunit rRNAs (5.8S, 5S, and 28S rRNAs):** These rRNAs provide the structural framework for the 60S subunit and contribute to the peptidyl transferase activity, which forms peptide bonds during protein synthesis.
- **60S ribosomal proteins:** Approximately 49 proteins associate with the rRNAs to form the functional 60S subunit. These proteins are involved in various functions, including mRNA binding, tRNA binding, and the regulation of translation initiation and elongation.

**mRNA:**
- **Messenger RNA (mRNA):** The template for protein synthesis, carrying the genetic code for a specific protein. It binds to the 40S subunit, allowing the ribosome to read the codons and translate them into an amino acid sequence.

**Initiator tRNA (Met-tRNAi):**
- **Transfer RNA carrying methionine (Met-tRNAi):** The first tRNA that binds to the ribosome during initiation. It carries the methionine amino acid, which will be the first amino acid of the newly synthesized protein.

**Initiation Factors (eIFs):**
- **eIF1:** Promotes the binding of mRNA to the 40S subunit and prevents premature association of the 60S subunit.
- **eIF1A:** Stabilizes the 40S subunit and promotes the binding of Met-tRNAi.
- **eIF2:** Binds Met-tRNAi and delivers it to the 40S subunit.
- **eIF3:** Binds to the 40S subunit and prevents its premature association with the 60S subunit.
- **eIF4A, eIF4B, eIF4E, eIF4G:** Involved in mRNA recognition, binding, and unwinding of secondary structures.
- **eIF5:** Promotes the joining of the 60S subunit to the 40S subunit, forming the 80S initiation complex.
- **eIF5B:** A GTPase that participates in the joining of the 60S subunit to the 40S subunit.

This complex assembly ensures the accurate initiation of protein synthesis, ensuring that the correct mRNA and initiator tRNA are positioned for translation.'
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Proteins (1)

Compounds (2)