GcrA Proteolysis in Caulobacter crescentus swarmer cells is ClpP-dependent

GcrA is responsible for the regulation of bacterial genes involved in motility, polar development, cell wall biogenesis, amino acid metabolism and transport, chromosome replication, repair, and recombination. Moreover, regulated proteolysis of proteins is a critical component of the bacterial cell cycle. The GcrA master regulator in Caulobacter crescentus accumulates in stalked cells but not in swarmer cells (although it is transcribed and translated in both cell types) because of swarmer-cell-specific proteolysis (Collier et al., 2006). We know that degradation of GcrA in swarmer cells is ClpP-dependent because when ClpP was depleted in swarmer cells, GcrA became more stable (Sean Murray, unpublished results). ClpP, with the help of chaperones, degrades regulatory and structural proteins to ensure the localization of polar organelles at the correct cell pole during correct time of the cell cycle. ClpP has two known chaperones, ClpA and ClpX. In this research we show that GcrA degradation in swarmer cells is ClpA independent. To test if ClpX is the chaperone, a ClpX depletion strain was created since clpX is an essential gene, but no change in GcrA accumulation was observed when ClpX was depleted. However, ClpX may have a higher affinity for GcrA than for other proteins that accumulate to toxic levels. A bypass suppressor screen was performed to see if a ClpX knockout could be viable. Such a strain would allow us to conclusively test if GcrA degradation is ClpX dependent. Unfortunately, no ClpX bypass suppressor was obtained.