Target type: biologicalprocess
The process preceding formation of the peptide bond between the first two amino acids of a protein in the cytoplasm. This includes the formation of a complex of the ribosome, mRNA or circRNA, and an initiation complex that contains the first aminoacyl-tRNA. [GOC:hjd]
Cytoplasmic translational initiation is the process by which ribosomes bind to mRNA and begin protein synthesis in the cytoplasm of eukaryotic cells. This intricate process involves several key steps:
1. **mRNA Binding:** Initiation begins with the mRNA molecule associating with the small ribosomal subunit (40S). The mRNA contains a 5' cap, a 5' untranslated region (5'UTR), a coding sequence (CDS), and a 3' untranslated region (3'UTR).
2. **Recruitment of Initiation Factors:** Initiation factors (eIFs) play critical roles in this process. eIF4F, a complex of eIF4E, eIF4A, and eIF4G, binds to the 5' cap of the mRNA. eIF4E interacts directly with the cap, while eIF4G serves as a scaffold, bridging eIF4E with eIF3, which is associated with the 40S subunit.
3. **Scanning for the Start Codon:** The 40S subunit, along with the bound initiation factors, moves along the mRNA in a 5' to 3' direction, searching for the start codon (AUG). This scanning process requires ATP hydrolysis and the helicase activity of eIF4A, which unwinds any secondary structures in the 5'UTR.
4. **tRNAi Met Binding:** A special initiator tRNA (tRNAi Met), carrying methionine, is bound to eIF2. This complex, known as the ternary complex (TC), also interacts with the 40S subunit. Once the start codon is located, the TC binds to the AUG codon.
5. **Large Subunit Joining:** The large ribosomal subunit (60S) joins the complex, forming the complete 80S ribosome. This step requires the hydrolysis of GTP and the release of several initiation factors.
6. **Initiation Complex Formation:** The fully assembled 80S ribosome, positioned at the start codon, is now ready to begin polypeptide elongation. The initiator methionine (Met) is positioned in the P site of the ribosome, primed for the next stage of translation.
Cytoplasmic translational initiation is tightly regulated, ensuring accurate translation of the correct mRNA and ensuring the correct initiation codon is identified. It is crucial for gene expression, as it sets the stage for the synthesis of functional proteins, essential for cellular processes.'
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| Protein | Definition | Taxonomy |
|---|---|---|
| Eukaryotic initiation factor 4A-II | A eukaryotic initiation factor 4A-II that is encoded in the genome of human. [PRO:DNx] | Homo sapiens (human) |
| Eukaryotic initiation factor 4A-I | A eukaryotic initiation factor 4A-I that is encoded in the genome of human. [PRO:DNx] | Homo sapiens (human) |
| Compound | Definition | Classes | Roles |
|---|---|---|---|
| cycloheximide | cycloheximide : A dicarboximide that is 4-(2-hydroxyethyl)piperidine-2,6-dione in which one of the hydrogens attached to the carbon bearing the hydroxy group is replaced by a 3,5-dimethyl-2-oxocyclohexyl group. It is an antibiotic produced by the bacterium Streptomyces griseus. Cycloheximide: Antibiotic substance isolated from streptomycin-producing strains of Streptomyces griseus. It acts by inhibiting elongation during protein synthesis. | antibiotic fungicide; cyclic ketone; dicarboximide; piperidine antibiotic; piperidones; secondary alcohol | anticoronaviral agent; bacterial metabolite; ferroptosis inhibitor; neuroprotective agent; protein synthesis inhibitor |
| rocaglamide | rocaglamide : An organic heterotricyclic compound that is 2,3,3a,8b-tetrahydro-1H-benzo[b]cyclopenta[d]furan substituted by hydroxy groups at positions 1 and 8b, methoxy groups at positions 6 and 8, a 4-methoxyphenyl group at position 3a, a phenyl group at position 3 and a N,N-dimethylcarbamoyl group at position 1. Isolated from Aglaia odorata and Aglaia duperreana, it exhibits antineoplastic activity. rocaglamide: RN refers to (1alpha,2alpha,3beta,3abeta,8bbeta)-isomer; isolated from stems of Aglaia elliptifolia; structure given in first source | monocarboxylic acid amide; monomethoxybenzene; organic heterotricyclic compound | antileishmanial agent; antineoplastic agent; metabolite |
| aglafoline | aglafolin : A heterotricyclic compound based on a 2,3,3a,8b-tetrahydro-1H-benzo[b]cyclopenta[d]furan framework substituted by hydroxy groups at positions C-1 and C-8b, a methoxycarbonyl group at C-2, a phenyl group at C-3, a 4-methoxyphenyl group at C-3a and methoxy groups at C-6 and C-8. A platelet aggregation inhibitor found in Aglaia elliptifolia and Aglaia odorata. aglafoline: a platelet activating factor antagonist; structure given in first source; isolated from Aglaia elliptifolia | methyl ester; organic heterotricyclic compound | metabolite; platelet aggregation inhibitor |
| hippuristanol | hippuristanol: from the gorgonian Isis hippuris | ||
| silvestrol | silvestrol : An organic heterotricyclic compound that consists of a 2,3,3a,8b-tetrahydro-H-benzo[b]cyclopenta[d]furan framework substituted by hydroxy groups at positions C-1 and C-8b, a methoxycarbonyl group at C-2, a phenyl group at C-3, a 4-methoxyphenyl group at C-3a, a methoxy group at C-8 and a 1,4-dioxan-2-yloxy group at position C-6 which in turn is substituted by a methoxy group at position 3 and a 1,2-dihydroxyethyl group at position 6. Isolated from Aglaia silvestris, it exhibits antineoplastic activity. silvestrol: isolated from the fruit and twig of Aglaia silvestris | dioxanes; ether; methyl ester; organic heterotricyclic compound | antineoplastic agent; metabolite |