Proline residues at the C terminus of nascent chains induce SsrA tagging during translation termination.
The SsrA or tmRNA quality control system relieves ribosome stalling and directs the addition of a degradation tag to the C terminus of the nascent chain. In some instances, SsrA tagging of otherwise full-length proteins occurs when the ribosome pauses at stop codons during normal translation termination. Here, the identities of the C-terminal residues of the nascent chain are shown to play an important role in full-length protein tagging. Specifically, a subset of C-terminal Xaa-Pro sequences caused SsrA tagging of the full-length YbeL protein from Escherichia coli. This tagging increased when a less efficient stop codon was used, increased in cells lacking protein release factor-3, and decreased when protein release factor-1 was overexpressed. Incorporation of the analog azetidine-2-carboxylic acid in place of proline suppressed tagging, whereas incorporation of 3,4-dehydroproline increased SsrA tagging of full-length YbeL. These results suggest that the detailed chemical or conformational properties of the C-terminal residues of the nascent polypeptide can affect the rate of translation termination, thereby influencing ribosome pausing and SsrA tagging at stop codons.
Hayes
Christopher S
CS
Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
Bose
Baundauna
B
Sauer
Robert T
RT
D018388:Codon, Terminator; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D011392:Proline / Q000378:metabolism*; D014176:Protein Biosynthesis; D011487:Protein Conformation; D012329:RNA, Bacterial / Q000737:chemistry / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*
D018388:Codon, Terminator; D029968:Escherichia coli Proteins; D012329:RNA, Bacterial; C096222:tmRNA; D011392:Proline