Understanding the posttranslational regulation of the response regulator RcsB and acetyl phosphate as an acetyl group donor in E. coli

The observation that Nepsilon-lysine acetylation occurs on a hundreds of proteins in bacteria is a recent discovery. To study the mechanisms that regulate acetylation and to determine if acetylation affects physiology, I studied the Escherichia coli response regulator and transcription factor RcsB, which was reported to be acetylated in vitro. To monitor RcsB activity, I measured transcription from the rprA promoter, which requires RcsB. I confirmed that RcsB is activated by phosphorylation through the Rcs phosphorelay and acetyl phosphate and showed that acetyl phosphate could phosphorylate RcsB. However, a mutant that accumulates acetyl phosphate (ackA) exhibited reduced rprA transcription instead of the predicted increase. To test if acetylation affected RcsB activity in vivo, I analyzed the effect of the only known E. coli protein deacetylase CobB on rprA transcription and RcsB acetylation and determined that the cobB mutant showed reduced rprA promoter activity and hyperacetylated RcsB. Perhaps more surprisingly, RcsB isolated from the ackA mutant was also hyperacetylated. Using a genetic approach, I identified an AckA- and CobB-sensitive RcsB lysine that controls its activity. Since RcsB acetylation increases when acetyl phosphate accumulates, we hypothesize that acetyl phosphate is a novel acetyl donor for protein acetylation.