期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 283, 期 34, 页码 22918-22929出版社
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M801692200
关键词
-
资金
- National Institutes of Health
Formation and degradation of SsrA-tagged proteins enable ribosome recycling and elimination of defective products of incomplete translation. We produced an antibody against the SsrA peptide and used it to measure the amounts of SsrA-tagged proteins in Escherichia coli cells without interfering with tagging or altering the context of the tag added at the ends of nascent polypeptides. SsrA-tagged proteins were present in very small amounts unless a component of the ClpXP protease was missing. From the levels of tagged proteins in cells in which degradation is essentially blocked, we calculate that >= 1 in 200 translation products receives an SsrA tag. ClpXP is responsible for >= 90% of the degradation of SsrA-tagged proteins. The degradation rate in wild type cells is >= 1.4 min(-1) and decreases to similar to 0.10 min(-1) in a clpX mutant. The rate of degradation by ClpXP is decreased similar to 3-fold in mutants lacking the adaptor SspB, whereas degradation by ClpAP is increased 3-5-fold. However, ClpAP degrades SsrA-tagged proteins slowly even in the absence of SspB, possibly because of interference from ClpA-specific substrates. Lon protease degrades SsrA-tagged proteins at a rate of similar to 0.05 min(-1) in the presence or absence of SspB. We conclude that ClpXP, together with SspB, is uniquely adapted for degradation of SsrA-tagged proteins and is responsible for the major part of their degradation in vivo.
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