The ClpXP and ClpAP proteases degrade proteins with carboxy-terminal peptide tails added by the SsrA-tagging system.
Interruption of translation in Escherichia coli can lead to the addition of an 11-residue carboxy-terminal peptide tail to the nascent chain. This modification is mediated by SsrA RNA (also called 10Sa RNA and tmRNA) and marks the tagged polypeptide for proteolysis. Degradation in vivo of lambda repressor amino-terminal domain variants bearing this carboxy-terminal SsrA peptide tag is shown here to depend on the cytoplasmic proteases ClpXP and ClpAP. Degradation in vitro of SsrA-tagged substrates was reproduced with purified components and required a substrate with a wild-type SsrA tail, the presence of both ClpP and either ClpA or ClpX, and ATP. Clp-dependent proteolysis accounts for most degradation of SsrA-tagged amino-domain substrates at 32 degrees C, but additional proteases contribute to the degradation of some of these SsrA-tagged substrates at 39 degrees C. The existence of multiple cytoplasmic proteases that function in SsrA quality-control surveillance suggests that the SsrA tag is designed to serve as a relatively promiscuous signal for proteolysis. Having diverse degradation systems able to recognize this tag may increase degradation capacity, permit degradation of a wide variety of different tagged proteins, or allow SsrA-tagged proteins to be degraded under different growth conditions.
Gottesman
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Laboratory of Molecular Biology, National Cancer Institute, Bethesda, Maryland 20892, USA. susang@helix.nih.gov
Roche
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Zhou
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Y
Sauer
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RT
D000251:Adenosine Triphosphatases; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D049071:Endopeptidase Clp; D004926:Escherichia coli / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D009154:Mutation; D021382:Protein Sorting Signals / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012329:RNA, Bacterial / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013379:Substrate Specificity; D013696:Temperature
D001426:Bacterial Proteins; D017931:DNA Primers; D029968:Escherichia coli Proteins; D021382:Protein Sorting Signals; D012329:RNA, Bacterial; D011993:Recombinant Fusion Proteins; C096222:tmRNA; D012697:Serine Endopeptidases; C483568:ClpA protease, E coli; C483573:ClpXP protease, E coli; D049071:Endopeptidase Clp; D000251:Adenosine Triphosphatases