The degradation of RcsA by ClpYQ(HslUV) protease in Escherichia coli

In Escherichia coli, RcsA, a positive activator for transcription of cps (capsular polysaccharide synthesis) genes, is degraded by the Lon protease. In lon mutant, the accumulation of RcsA leads to overexpression of capsular polysaccharide. In a previous study, overproduction of ClpYQ(HslUV) protease represses the expression of cpsBlacZ, but there has been no direct observation demonstrating that ClpYQ degrades RcsA. By means of a MBP-RcsA fusion protein, we showed that RcsA activated cpsBlacZ expression and could be rapidly degraded by Lon protease in SG22622 (lon⁺). Subsequently, the comparative half-life experiments performed in the bacterial strains SG22623 (lon) and AC3112 (lon clpY clpQ) indicated that the RcsA turnover rate in AC3112 was relatively slow and RcsA was stable at 30 °C or 41 °C. In addition, ClpY could interact with RscA in an in vitro pull-down assay, and the more rapid degradation of RcsA was observed in the presence of ClpYQ protease at 41 °C. Thus, we conclude that RcsA is indeed proteolized by ClpYQ protease.