RESUMO
The Escherichia coli starvation-induced DNA protection protein Dps was observed to be degraded rapidly during exponential growth. This turnover is dependent on the clpP and clpX genes. The clpA gene is not required for Dps proteolysis, suggesting that Dps is a substrate for ClpXP protease but not for ClpAP protease. Dps proteolysis was found to be highly regulated. Upon carbon starvation, Dps is stabilized, which together with increased Dps synthesis allows strong accumulation of Dps in the stationary phase. The addition of glucose to starving cells results in rapid resumption of Dps proteolysis by ClpXP. Oxidative stress also leads to efficient stabilization of Dps. After hyperosmotic shift, however, proteolysis remains unaffected. Thus, regulated proteolysis of Dps strongly contributes to controlling Dps levels under very specific stress conditions. In contrast to the regulated degradation of RpoS by ClpXP, Dps proteolysis is independent of the recognition factor RssB. In addition, during starvation, clpP and, to a somewhat lesser extent, clpA are involved in maintaining ongoing Dps synthesis (acting at the level of Dps translation), which is required for strong Dps accumulation in long-term stationary phase cells. In summary, both ClpXP and ClpAP exert significant control of Dps levels by affecting log phase stability and stationary phase synthesis of Dps respectively.
