Journal of Bacteriology, January 2001, p. 155-161, Vol. 183, No. 1
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.1.155-161.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Department of Applied Biochemistry, Kyoto Prefectural University, Shimogamo, Sakyo, Kyoto 606-8522, Japan
Received 13 April 2000/Accepted 10 October 2000
HrcA, a negative control repressor for chaperone expression from the obligate thermophile Bacillus thermoglucosidasius KP1006, was purified in a His-tagged form in the presence of 6 M urea but hardly renatured to an intact state due to extreme insolubility. Renaturation trials revealed that the addition of DNA to purified B. thermoglucosidasius HrcA can result in solubilization of HrcA free from the denaturing agent urea. Results from band shift and light scattering assays provided three new findings: (i) any species of DNA can serve to solubilize B. thermoglucosidasius HrcA, but DNA containing the CIRCE (controlling inverted repeat of chaperone expression) element is far more effective than other nonspecific DNA; (ii) B. thermoglucosidasius HrcA renatured with nonspecific DNA bound the CIRCE element in the molecular ratio of 2.6:1; and (iii) B. thermoglucosidasius HrcA binding to the CIRCE element was stable at below 50°C whereas the complex was rapidly denatured at 70°C, suggesting that the breakdown of HrcA is induced by heat stress and HrcA may act as a thermosensor to affect the expression of heat shock regulatory genes. These results will help to determine the nature of HrcA protein molecules.
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