Necessary for the transition from vegetative growth to stage 0 or stage II of sporulation, but sporulation subsequent to these stages is unaffected at 45 degrees Celsius. This ts effect is probably due solely to the E-79 mutation. Required for expression of early sporulation genes, further suggesting a role in the induction of sporulation. Depletion effects on sporulation can be partially suppressed by missense mutations in spo0A. Strains depleted for obg stop growing after about 3 hours and do not induce the sigma-B factor following ethanol stress. It cofractionates with the ribosome and upstream stress response regulators RsbR, RsbS and RsbT in size fractionation columns, suggesting the ribosome might serve as a possible mediator of the activity of obg and the stress induction of sigma-B. In glycerol gradients partially associates with ribosomes; this is stabilized by a nonhydrolyzable GTP-analog and to a lesser extent GTP and GDP. An essential GTPase which binds GTP, GDP and possibly (p)ppGpp with moderate affinity, with high nucleotide exchange rates and a fairly low GTP hydrolysis rate. Plays a role in control of the cell cycle, stress response, ribosome biogenesis and in those bacteria that undergo differentiation, in morphogenesis control. Inhibited by GDP; less than 20 uM ppGpp stimulates the GTPase, while higher concentrations inhibit. Turnover number of 0.0061/min. Monomer. Interacts with TasA (AC P54507) in pull-down experiments. Cofractionates with the ribosome and stress response regulators RsbR, RsbS and RsbT in size fractionation columns; binds to ribosomal protein L13. Part of an operon with spo0B. A mutant in the N-terminal obg domain (Asp-92) impairs growth and ribosome association but has no effect on sporulation or the general stress regulon (GSR). Replacing the last 22 amino acids has no effect on growth or ribosome association, but eliminates sporulation and reduces the GSR, showing for the first time that growth promotion and the GSR phenotypes are separable. Essential for growth, it cannot be disrupted. In depletion experiments cells become over 3-fold longer, are abnormally curved and nucleoids condense. Estimated to be present at 6000 copies per cell. Belongs to the TRAFAC class OBG-HflX-like GTPase superfamily. OBG GTPase family.