An abundant, essential GTPase which binds GTP, GDP and ppGpp with moderate affinity. Has high guanosine nucleotide exchange rate constants for GTP and GDP, and a relatively low GTP hydrolysis rate stimulated by the 50S ribosomal subunit. It is estimated there are 34000 molecules in log-phase cells and 5600 molecules in stationary-phase cells. Required for chromosome segregation. Plays a role in the stringent response, perhaps by sequestering 50S ribosomal subunits and decreasing protein synthesis (PubMed:19555460), and a non-essential role in the late steps of ribosome biogenesis, perhaps acting as a checkpoint for correct 50S subunit synthesis (Probable) (PubMed:24844575). Overexpression increases bacterial persistence (in exponential and stationary phase) in response to antibiotics (PubMed:26051177). Cells expressing high levels of Obg are more likely to form persister cells upon antibiotic exposure; this requires alarmone (p)ppGpp and acts via induced HokB, depolarizing cells, which probably reduces metabolic activity and induces persistence (PubMed:26051177). The persister phenotype can be separated from the essential phenotype (PubMed:26051177). Required for correct chromosome partitioning; in temperature-sensitive (ts) mutant nucleoids do not partition but remain in the middle of cell, cells elongate but do not divide. Overexpression protects cells against UV damage. Ts mutants have impaired plasmid and lamdba phage replication, possibly via effects on DnaA (PubMed:12826057). Regulates DnaA levels. Genetic interactions of Val-168 and a C-terminal insertion mutant with the double-strand break repair factors recA and recBCD, and with seqA suggests that ObgE, either directly or indirectly, promotes replication fork stability (PubMed:15721258). May protect replication forks from stress induced by toxic levels of hydroxyl radicals (PubMed:22863262). Initiation of DNA replication continues in ObgE-depleted cells. Binds to pre-50S ribosomal subunits in a salt-dependent manner. Acts as a ribosome anti-association factor; guanosine nucleotides stimulate ObgE 50S subunit binding and also ObgE-mediated 70S ribosome dissociation (GDP<GTP<GMP-PNP<ppGpp) (PubMed:24844575). Overexpression rescues an rrmJ deletion stabilizing the 70S ribosome. Even at permissive temperatures the ts mutant (Gln-80/Asn-85) shows disrupted 50S ribosomal subunit assembly, defects in 16 and 23S rRNA processing and altered association of some late-assembling ribosomal proteins (PubMed:11555285). Dissociates from the pre-50S ribosome under conditions of amino acid starvation. The levels of (p)ppGpp rise in the ts mutant (Gln-80/Asn-85), possibly because ObgE controls SpoT. Binds GDP and ppGpp with the same affinity. During ribosome assembly ObgE acts later than the rRNA methyltransferase RrmJ and DEAD-box RNA helicases DeaD and SrmB. Turnover number of 0.02/min. Monomer. Binds to the intersubunit face of the 50S ribosomal subunit where translation factors bind, protruding into the peptidyl-transfer center, leading to significant changes in both ObgE and 50S ribosome structure (PubMed:24844575). Associates with SpoT (PubMed:15292126, PubMed:17616600). Binding to 50S ribosomes does not require SpoT. 50S ribosomal subunit binding is enhanced by guanosine nucleotides (PubMed:24844575). The majority is associated with the 50S ribosomal subunit (PubMed:15292126), another group also sees association with 30S subunit (PubMed:15836769). Constitutively expressed, levels decrease toward stationary phase (at protein level). Induced in a dose-dependent manner by UV irradiation. The C-terminus (residues 341-390) is not required for either 50S ribosome subunit association nor 70S ribosome dissociation. Essential for growth, it cannot be disrupted. Belongs to the TRAFAC class OBG-HflX-like GTPase superfamily. OBG GTPase family.