Translation Termination and Ribosome Recycling in Eukaryotes

Abstract

Termination of mRNA translation occurs when a stop codon enters the A site of the ribosome, and in eukaryotes is mediated by release factors eRF1 and eRF3, which form a ternary eRF1/eRF3-guanosine triphosphate (GTP) complex. eRF1 recognizes the stop codon, and after hydrolysis of GTP by eRF3, mediates release of the nascent peptide. The post-termination complex is then disassembled, enabling its constituents to participate in further rounds of translation. Ribosome recycling involves splitting of the 80S ribosome by the ATP-binding cassette protein ABCE1 to release the 60S subunit. Subsequent dissociation of deacylated transfer RNA (tRNA) and messenger RNA (mRNA) from the 40S subunit may be mediated by initiation factors (priming the 40S subunit for initiation), by ligatin (eIF2D) or by density-regulated protein (DENR) and multiple copies in T-cell lymphoma-1 (MCT1). These events may be subverted by suppression of termination (yielding carboxy-terminally extended read-through polypeptides) or by interruption of recycling, leading to reinitiation of translation near the stop codon.

Translation arrest as a protein quality control system for aberrant translation of the 3′‐UTR in mammalian cells

“…To further investigate the effects of the C-end degron, we constructed the RLUC-X-(Ser) 3 -STOP reporter, in which three alanine residues at the C-terminal end were substituted by serine residues, which are not recognized as a C-end degron. Of 19 genes tested, RLUC-DHCR7-(Ser) 3 was the only protein expressed at a higher level than RLUC-DHCR7-(Ala) 3 (Fig. 3D, lane 19), and the levels of RLUC-X-(Ser) 3 -STOP reporter mRNAs were the essentially the same as that of RLUC-X-(Ala) 3 -STOP mRNAs (Fig.…”

“…C-terminal alanine residues function as a 'C-end degron' that is recognized by Cullin-RING E3 ubiquitin ligase (CRL) complex adaptors or computationally implicated multiple non-CRLs, and proteins with the 'C-end degron' are subjected to proteasome-dependent degradation [37,38]. To examine the possible effects of the C-end degron, cells were treated with MG132, which upregulated RLUC-X-(Ala) 3 proteins containing a C-terminal extension derived from the 3 0 -UTRs of KCNV2, ACTA1, DHCR7, and SLC26A4 (Fig. 3B, lanes 12, 14, 40, and 46, respectively).…”

“…Protein synthesis is a fundamental process for all living species. Termination of translation at a stop codon is an essential step ensuring accurate protein expression . However, ribosomes stochastically read through a stop codon in the presence of errors or genetic mutations.…”

“…Effects of 3 0 -UTR translation on protein and mRNA expression. (A) Schematic drawing of the RLUC-X-(x)3 -STOP reporter. The large X represents the region of the inserted 3 0 -UTR sequence, and the small x represents the region of the C-end tag (Ala-Ala-Ala or Ser-Ser-Ser).…”

Selective Translation Complex Profiling Reveals Staged Initiation and Co-translational Assembly of Initiation Factor Complexes

“…These fragmented complexes produce a higher proportion of the smaller FP-type than seen in the 80S FP libraries ( Figure S7A,B), consistent with a lower crosslinking efficiency for 80Ses with an empty A site. The 40S FPs also accumulate at stop codons ( Figure S2A, right-handed panel), likely representing authentic intermediates of staged 80S recycling, wherein the 60S subunit (60S) is recycled to leave a 40S post-termination complex for the second stage of recycling (Hellen, 2018). Of note, 5'UTR 40S coverage, which should represent primarily scanning PICs, extends up to the mRNA 5' ends ( Figure 2B and Figure S7F).…”