Recombinant Escherichia coli GTPase ObgE/CgtA (obgE)

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, and a non-essential role in the late steps of ribosome biogenesis, perhaps acting as a checkpoint for correct 50S subunit synthesis (Probable). Overexpression increases bacterial persistence (in exponential and stationary phase) in response to antibiotics. 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. The persister phenotype can be separated from the essential phenotype.; 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. 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. May protect replication forks from stress induced by toxic levels of hydroxyl radicals. 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