Translocon “Pulling” of Nascent SecM Controls the Duration of Its Translational Pause and Secretion-Responsive
            <i>secA</i>
            Regulation

Butkus, Martha E.; Prundeanu, Lucia; Oliver, Donald B.

doi:10.1128/jb.185.22.6719-6722.2003

Cited by 99 publications

(91 citation statements)

References 23 publications

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“…Although the elongation arrest of SecM is released soon in normal cells, presumably by the pulling force generated by the nascent chain translocation across the membrane (11,12,14,36), our results now demonstrated that even such transient arrest is important for E. coli to express SecA at sufficient levels. Indeed, mutational alterations of the arrest-important amino acid residues in SecM reduced the expression of the cis-located secA gene.…”

Section: Discussionmentioning

confidence: 72%

“…In normal cells, in which the N-terminal part of the nascent SecM is pulled by the Sec translocase, the elongation arrest is soon released, whereas the arrest is strikingly prolonged under conditions in which the translocation machinery or the SecM signal sequence is functionally defective (11,14,15). Although it is believed that the stalled ribosome will disrupt the secondary structure of the secM-secA mRNA to allow the easier entry of new ribosomes that translate secA, the importance of SecM elongation arrest in basal and regulated secA expression has not been established.…”

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confidence: 99%

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Translation arrest of SecM is essential for the basal and regulated expression of SecA

Murakami

Nakatogawa

Ito

2004

Proc. Natl. Acad. Sci. U.S.A.

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The SecM protein of Escherichia coli contains an arrest sequence (F 150 XXXXWIXXXXGIRAGP 166 ), which interacts with the ribosomal exit tunnel to halt translation elongation beyond Pro-166. This inhibition is reversed by active export of the nascent SecM chain. Here, we studied the physiological roles of SecM. Arrest-alleviating mutations in the arrest sequence reduced the expression of secA, a downstream gene on the same mRNA. Among such mutations, the arrest-abolishing P166A substitution mutation on the chromosomal secM gene proved lethal unless the mutant cells are complemented with excess SecA. Whereas secretion defect due either to azide addition, a secY mutation, or low temperature leads to up-regulated SecA biosynthesis, this regulation was lost by a secM mutation, which synergistically retarded growth of cells with lowered secretion activity. Finally, an arrest-alleviating rRNA mutation affecting the constricted part of the exit tunnel lowered the basal level of SecA as well as its secretion defect-induced upregulation. Thus, the arrest sequence of SecM has at least two roles in SecA translation. First, the transient elongation arrest in normal cells is required for the synthesis of SecA at levels sufficient to support cell growth. Second, the prolonged SecM elongation arrest under conditions of unfavorable protein secretion is required for the enhanced expression of SecA to cope with such conditions.

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Section: Discussionmentioning

confidence: 72%

mentioning

confidence: 99%

Translation arrest of SecM is essential for the basal and regulated expression of SecA

Murakami

Nakatogawa

Ito

2004

Proc. Natl. Acad. Sci. U.S.A.

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“…Two possibilities have been proposed (6). In the physical/pulling model, physical force generated by the protein localization reaction triggers the release reaction (25). In the signal transmission model, interaction of the ribosome-nascent chain complex with the protein delivery machinery induces intraribosomal signal transmission to affect the peptidyl transferase center of the ribosome.…”

Section: Discussionmentioning

confidence: 99%

Recruitment of a species-specific translational arrest module to monitor different cellular processes

Chiba

Kanamori

Ueda

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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Nascent chain-mediated translation arrest serves as a mechanism of gene regulation. A class of regulatory nascent polypeptides undergoes elongation arrest in manners controlled by the dynamic behavior of the growing chain; Escherichia coli SecM monitors the Sec protein export pathway and Bacillus subtilis MifM monitors the YidC membrane protein integration/folding pathway. We show that MifM and SecM interact with the ribosome in a speciesspecific manner to stall only the ribosome from the homologous species. Despite this specificity, MifM is not exclusively designed to monitor membrane protein integration because it can be converted into a secretion monitor by replacing the N-terminal transmembrane sequence with a secretion signal sequence. These results show that a regulatory nascent chain is composed of two modular elements, one devoted to elongation arrest and another devoted to subcellular targeting, and they imply that physical pulling force generated by the latter triggers release of the arrest executed by the former. The combinatorial nature may assure common occurrence of nascent chain-mediated regulation.stalling sequence | SpoIIIJ | SecA | exit tunnel

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“…A secondary structure encompassing the secA Shine-Dalgarno sequence of the secM-secA-mutT RNA can conditionally inhibit secA translation. Due to its arrest sequence, secM translation stalls when its N-terminal signal sequence is not "pulled" by the protein export machinery (7,8). Paused ribosomes are thought to mediate unfolding of the RNA secondary structure, thereby exposing the initiation signal for SecA biosynthesis (9).…”

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confidence: 99%

SsrA Tagging of Escherichia coli SecM at Its Translation Arrest Sequence

Collier

Bohn

Bouloc

2004

Journal of Biological Chemistry

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SecM is expressed from the secM-secA operon and activates the expression of secA in response to secretion defects. The 3 -end of secM encodes an "arrest sequence," which can interact with the ribosomal exit tunnel, preventing complete secM translation under secretion-defective conditions. In a cis-acting manner, ribosome stalling enhances secA translation. Pro 166 is the last residue incorporated when SecM elongation is arrested. We report that secretion deficiencies lead to SsrA tagging of SecM after Pro 166 , Gly 165 , and likely Arg 163 . Northern blot analysis revealed the presence of a truncated secM transcript, likely issued from a secMsecA cleavage. The level of secM transcripts was decreased either when secM translation was totally prevented or when Pro 166 was mutated. However, the accumulation of a truncated secM transcript required secM translation and was prevented when the SecM arrest sequence was inactivated by a point mutation changing Pro 166 to Ala. We suggest that ribosome pausing at the site encoding the arrest sequence is required for formation of the truncated secM mRNA. SsrA tagging affected neither the presence of the secM mRNA nor secA expression, even under translocation-defective conditions. It is therefore likely that SsrA tagging of SecM occurs only after cleavage of secM-secA mRNA within the secM open reading frame encoding the SecM arrest sequence. Accumulation of transcripts expressing arrested SecM generated growth inhibition that was alleviated by the SsrA tagging system. Therefore, SsrA tagging of SecM would rescue ribosomes to avoid excessive jamming of the translation apparatus on stop-less secM mRNA. Nascent proteins emerge from the 50 S ribosomal subunit through an exit tunnel with a length of ϳ100 Å and containing 35-40 amino acids of the elongating polypeptide. Its narrowness prevents peptide folding, and certain sequences from nascent peptides can interact with ribosomal elements of the tunnel to affect protein biosynthesis. The ribosome is therefore sensitive to the composition of the amino acid chain it is synthesizing, and the exit tunnel contributes to the dynamics of protein elongation (1). In Escherichia coli, this is exemplified by a sequence of the periplasmic protein SecM (secretion monitor) at a position close to its C terminus called the arrest sequence, which interacts with the ribosomal exit tunnel and causes elongation arrest within the ribosome (Refs. 2 and 3; for review, see Refs. 4 and 5). Ribosomal arrest is a key element in the regulation of SecA, an ATPase that targets protein precursors to the SecYEG core translocon for secretion. SecA is expressed from the secM-secA-mutT operon; its translation is up-regulated by a block in SecM secretion in a cis-specific manner (2, 6). A secondary structure encompassing the secA Shine-Dalgarno sequence of the secM-secA-mutT RNA can conditionally inhibit secA translation. Due to its arrest sequence, secM translation stalls when its N-terminal signal sequence is not "pulled" by the protein export machinery (7,8). Pau...

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Translocon “Pulling” of Nascent SecM Controls the Duration of Its Translational Pause and Secretion-Responsive secA Regulation

Cited by 99 publications

References 23 publications

Translation arrest of SecM is essential for the basal and regulated expression of SecA

Translation arrest of SecM is essential for the basal and regulated expression of SecA

Recruitment of a species-specific translational arrest module to monitor different cellular processes

SsrA Tagging of Escherichia coli SecM at Its Translation Arrest Sequence

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