IBPA AND IBPB, THE NEW HEAT-SHOCK PROTEINS, BIND TO ENDOGENOUS ESCHERICHIA COLI PROTEINS AGGREGATED INTRACELLULARLY BY HEAT SHOCK

摘要

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; Alien 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). [References: 25]