Pathway · 12 proteins
Translation cycle
Initiation, elongation and release factors support decoding and chain synthesis.
How it works
- Initiation places the message, initiator tRNA and ribosomal subunits in the appropriate arrangement.
- During elongation, charged tRNA delivery, peptide-bond formation and translocation advance the growing polypeptide along the message.
- A stop codon recruits release factors. Termination releases the chain; recycling prepares the machinery for another round.
Grouped by the atlas’s curated pathway map. The table order is not a proven reaction order.
Its proteins
| Protein | EC | Reaction (UniProt) | Metal or cluster | Amino acids | Certainty |
|---|---|---|---|---|---|
| Elongation factor G | — | — | — | 699 | Step named |
| Elongation factor Tu | 3.6.5.3 | GTP + H2O = GDP + phosphate + H(+) | Mg(2+) | 405 | Step named |
| Release factor glutamine methyltransferase | 2.1.1.297 | L-glutaminyl-[peptide chain release factor] + S-adenosyl-L-methionine = N(5)-methyl-L-glutaminyl-[peptide chain release factor] + S-adenosyl-L-homocysteine + H(+) | — | 281 | Step named |
| Selenocysteine-specific elongation factor | — | — | Mg(2+) | 582 | System only |
| Elongation factor P | — | — | — | 192 | Step named |
| Elongation factor 4 | 3.6.5.n1 | GTP + H2O = GDP + phosphate + H(+) | — | 600 | Step named |
| Translation initiation factor IF-3 | — | — | — | 175 | Step named |
| Peptide chain release factor 2 | — | — | — | 373 | Step named |
| Translation initiation factor IF-2 | — | — | — | 805 | Step named |
| Elongation factor Ts | — | — | — | 290 | Step named |
| Elongation factor P--(R)-beta-lysine ligase homolog | — | — | — | 293 | Step named |
| Peptide chain release factor 1 | — | — | — | 362 | Step named |
Origins
How could proteins be made before the factors that start, extend and end each chain existed?
Asked since the late 1960s by Woese, Crick and Orgel: how could the first translation system have arisen without proteins? The RNA world is the usual answer, with RNA doing the jobs proteins do now.
Besides the ribosome itself, translation needs separate protein factors to start, extend, end and recycle; the authors in RNA Worlds ask how the first ribosome could have depended on proteins. Alberts states the paradox: nucleic acids are needed to make proteins, and proteins are needed to make nucleic acids.
EF-Tu, for example, delivers each charged tRNA and must be recharged with GTP by another factor after every delivery. Twelve proteins of the minimal set drive this cycle.
From the books: Atkins, Gesteland & Cech (eds.), RNA Worlds, p. 143; Alberts et al., Molecular Biology of the Cell, p. 389; Horton et al., Principles of Biochemistry, p. 771.
The wider question for this part of the cell: origins for building proteins and folding them.
Sources
- Atlas pathway grouping from the VF5 reference-genome system map (Deckert et al. 1998; Braakman & Smith 2014)
Other pathways in this group: Ribosomal subunits · Translation interface · RNA maturation · Protein translocation · Protein turnover · Folding and stabilization · Recycling and rescue · Early folding support · Protein targeting · Ribosome · Protein export · Not yet placed in a pathway