IbpA and IbpB, the new heat-shock proteins, bind to endogenous Escherichia coli proteins aggregated intracellularly by heat shock.
IbpA/B, 16 kDa heat-shock proteins were recently described as recognizing heterologous protein inclusion bodies in Escherichia coli cells; the corresponding genes formed an operon regulated by the rpoH gene product, sigma 32 protein (Burland et al (1993) Genomics 16, 551; Allen et al (1992) J Bacteriol 174, 6938; Chuang et al (1993) Gene 134, 1; Chuang and Blattner (1993) J Bacteriol 175, 5242). We have found that IbpA/Bs also recognize endogenous bacterial proteins aggregated intracellularly by heat shock. IbpA/B proteins were isolated and purified from the aggregates (the S fraction), identified by amino acid microsequencing and used as immunogen for anti-IbpA/B serum preparation. Western blotting with the serum showed that in cells growing at 30 degrees C IbpA/B were located in the bacterial outer membrane and appeared in the S fraction after heat shock. Then the cellular level of the IbpA/B proteins increased about 20-fold as estimated by densitometry of the Western blots. In the E coli rpoH strain the level of IbpA/B was higher than in wild type before the heat shock and rose to still higher levels after it. This result pointed to a regulation of ibpA/B operon by another factor, besides that of sigma 32.
Laskowska
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Department of Biochemistry, University of Gdańsk, Poland.
Wawrzynów
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Taylor
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D001426:Bacterial Proteins / Q000378:metabolism*; D002449:Cell Aggregation; D002458:Cell Fractionation; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism*; D002479:Inclusion Bodies / Q000378:metabolism*; D007525:Isoelectric Focusing; D008970:Molecular Weight
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; C097578:IbpA protein, E coli; C097579:IbpB protein, E coli