Identification of an essential Caulobacter crescentus gene encoding a member of the Obg family of GTP-binding proteins.

We have identified an essential Caulobacter crescentus gene (cgtA) that encodes a member of a recently identified subfamily of GTPases (the Obg family) conserved from Bacteria to Archaea to humans. This evolutionary conservation between distantly related species suggests that this family of GTP-binding proteins possesses a fundamental, yet unknown, cellular role. In this report, we describe the isolation and sequence of the cgtA gene. The predicted CgtA protein displays striking similarity to the Obg family of small, monomeric GTP-binding proteins, both in the conserved guanine nucleotide-binding domains and throughout the N-terminal glycine-rich domain that is found in many members of the Obg family. Disruption of the cgtA gene was lethal, demonstrating that this gene is essential for cell growth. Immunoblot analysis revealed that CgtA protein levels remained constant throughout the C. crescentus cell cycle.