Phenotypic investigations of the depletion of EngA in Escherichia coli are consistent with a role in ribosome biogenesis

The EngA protein is a conserved and essential bacterial GTPase of largely enigmatic function. While most investigations of EngA have suggested a role in ribosome assembly, the protein has also been implicated in diverse elements of physiology including chromosome segregation, cell division, and cell cycle control. Here, we have probed additional phenotypes related to ribosome biogenesis on depletion of EngA in Escherichia coli to better understand its role in the cell. Depletion of EngA resulted in cold-sensitive growth and stimulation of a ribosomal rRNA promoter, both phenotypes associated with the disruption of ribosome biogenesis in bacteria. Among antibiotics that inhibit translation, depletion of EngA resulted in sensitization to the aminoglycoside class of antibiotics. EngA bound the alarmone ppGpp with equally high affinity as it bound GDP. These data offer additional support for a role in ribosome biogenesis for EngA, possibly in maturation of the A-site of the 50S subunit.