N GreA and thioredoxins, we propose that they may share a similar mechanism regarding their chaperone functions. There are approximately 13,800 molecules of GreA in each Bacillus subtilis cell, which is nearly twice that of RNAP levels and far more than that of other transcription factors [34]. The distribution of highly concentrated GreA molecules in the cell may engender an effective chaperone buffer like DnaK and other chaperones. In turn, this would help to prevent protein aggregation, promote renaturation of denatured proteins, and thus enhance cellular resistance to stress. Our result that the temperature sensitive greA/greB double mutant strain suffers more extensive protein aggregation suggests that GreA may act as chaperone in vivo. Increased expression of GreA under acidic stress [13] and the enhanced heat-shock survival rate of the GreAoverexpressing strain provide extra evidence for such activity. Deletion of greA results in sensitivity to salt stress [14,15] and double-deletion of greA and greB causes heat sensitivity [17], which suggest that GreA plays a 15481974 critical role in stress resistance. Owing to the chaperone activity of GreA, we infer that GreA may protect or stabilize RNAP in stressful conditions. If this is one of the major roles of GreA, we predict that RNAP should be one of its natural substrates. We further propose that GreA may play a novel role in the transcription apparatus. Interestingly, 
the Database of Interaction Protein (DIP) (http://dip.doe-mbi.ucla.edu/dip/ Main.cgi) shows that GreA interacts directly with ribosome subunits, such as DnaK, DnaJ, GroES, ClpX, and other chaperones in vivo, suggesting the existence of potentially important relationships between GreA and the molecular chaperone system. In conclusion, this study may provide the first evidence that indicates a link between the transcription apparatus and protein quality control.and eluted with the elution buffer (20 mM sodium phosphate, 0.5 M NaCl, 500 mM imidazole, pH 7.4). The solution was then loaded on a BTZ043 site Desalting column to get rid of imidazoles and excess salts.Effect on heat-induced aggregationADH from Saccharomyces cerevisiae and aldolase from rabbit muscle were used as substrate proteins to test the suppression effect of GreA on heat-induced aggregation. ADH bought from Sigma was diluted to 1 mM in 50 mM phosphate buffer (pH 7.4) and incubated at 48uC with different concentrations of GreA protein (0.2 mM, 0.5 mM, 1 mM, 2 mM). DnaK of 2 mM was also added as a control. The aggregation was monitored by detecting the optical density at 360 nm of the samples in an Ultrospec 2100 spectrophotometer (Amersham Biosciences). Aldolase (GE Healthcare) was also diluted to 1 mM in 50 mM phosphate buffer (pH 7.4) and incubated at 50uC to induce aggregation. Various concentrations of 
GreA were added (0.5 mM, 1 mM, 2 mM), and aggregation was monitored as described above.Protection of enzymatic activityADH was diluted to 0.3 mM in 12926553 50 mM phosphate buffer (pH 7.4) with different concentrations of GreA (0.3 mM, 0.6 mM, 1.2 mM) or 1 mM DnaK added. Denaturation was induced by incubation in a 50uC water bath. After incubation for 80 min, the ADH activity was measured in reaction mixtures containing 50 mM phosphate buffer (pH 10.5), 5 mM NAD, and 5 mM ethanol. The reaction was started by adding ADH, and reduction of NAD was detected by the 374913-63-0 increase in absorbance at 360 nm.Reactivation of chemical denatured proteinsGFP was denatured at 100 mM in 0.12 M HCl for 6.N GreA and thioredoxins, we propose that they may share a similar mechanism regarding their chaperone functions. There are approximately 13,800 molecules of GreA in each Bacillus subtilis cell, which is nearly twice that of RNAP levels and far more than that of other transcription factors [34]. The distribution of highly concentrated GreA molecules in the cell may engender an effective chaperone buffer like DnaK and other chaperones. In turn, this would help to prevent protein aggregation, promote renaturation of denatured proteins, and thus enhance cellular resistance to stress. Our result that the temperature sensitive greA/greB double mutant strain suffers more extensive protein aggregation suggests that GreA may act as chaperone in vivo. Increased expression of GreA under acidic stress [13] and the enhanced heat-shock survival rate of the GreAoverexpressing strain provide extra evidence for such activity. Deletion of greA results in sensitivity to salt stress [14,15] and double-deletion of greA and greB causes heat sensitivity [17], which suggest that GreA plays a 15481974 critical role in stress resistance. Owing to the chaperone activity of GreA, we infer that GreA may protect or stabilize RNAP in stressful conditions. If this is one of the major roles of GreA, we predict that RNAP should be one of its natural substrates. We further propose that GreA may play a novel role in the transcription apparatus. Interestingly, the Database of Interaction Protein (DIP) (http://dip.doe-mbi.ucla.edu/dip/ Main.cgi) shows that GreA interacts directly with ribosome subunits, such as DnaK, DnaJ, GroES, ClpX, and other chaperones in vivo, suggesting the existence of potentially important relationships between GreA and the molecular chaperone system. In conclusion, this study may provide the first evidence that indicates a link between the transcription apparatus and protein quality control.and eluted with the elution buffer (20 mM sodium phosphate, 0.5 M NaCl, 500 mM imidazole, pH 7.4). The solution was then loaded on a Desalting column to get rid of imidazoles and excess salts.Effect on heat-induced aggregationADH from Saccharomyces cerevisiae and aldolase from rabbit muscle were used as substrate proteins to test the suppression effect of GreA on heat-induced aggregation. ADH bought from Sigma was diluted to 1 mM in 50 mM phosphate buffer (pH 7.4) and incubated at 48uC with different concentrations of GreA protein (0.2 mM, 0.5 mM, 1 mM, 2 mM). DnaK of 2 mM was also added as a control. The aggregation was monitored by detecting the optical density at 360 nm of the samples in an Ultrospec 2100 spectrophotometer (Amersham Biosciences). Aldolase (GE Healthcare) was also diluted to 1 mM in 50 mM phosphate buffer (pH 7.4) and incubated at 50uC to induce aggregation. Various concentrations of GreA were added (0.5 mM, 1 mM, 2 mM), and aggregation was monitored as described above.Protection of enzymatic activityADH was diluted to 0.3 mM in 12926553 50 mM phosphate buffer (pH 7.4) with different concentrations of GreA (0.3 mM, 0.6 mM, 1.2 mM) or 1 mM DnaK added. Denaturation was induced by incubation in a 50uC water bath. After incubation for 80 min, the ADH activity was measured in reaction mixtures containing 50 mM phosphate buffer (pH 10.5), 5 mM NAD, and 5 mM ethanol. The reaction was started by adding ADH, and reduction of NAD was detected by the increase in absorbance at 360 nm.Reactivation of chemical denatured proteinsGFP was denatured at 100 mM in 0.12 M HCl for 6.
