Chromosome segregation control by Escherichia coli ObgE GTPase

Abstract

SummaryEscherichia coli cells depleted of the conserved GTPase, ObgE, show early chromosome-partitioning defects and accumulate replicated chromosomes in which the terminus regions are colocalized. Cells lacking ObgE continue to initiate replication, with a normal ratio of the origin to terminus. Localization of the SeqA DNA binding protein, normally seen as punctate foci, however, was disturbed. Depletion of ObgE also results in cell filamentation, with polyploid DNA content. Depletion of ObgE did not cause lethality, and cells recovered fully after expression of ObgE was restored. We propose a model in which ObgE is required to license chromosome segregation and subsequent cell cycle events.

Towards an Elucidation of the Roles of the Ribosome during Different Growth Phases inBacillus subtilis

“…On the other hand, the results of three separate studies indicated that Obg, as well as its orthologs in many bacteria, is required for the assembly of the 50S subunit, [48][49][50] even though it has been found in E. coli that ObgE (an Obg ortholog) plays a direct role in chromosome segregation and that the ribosome assembly phenotype is a secondary effect. 51) In addition, Obg co-elutes with the ribosome and is bound specifically to ribosomal protein L13, together with other factors that are involved in the general stress response. 52) These results suggest that Obg might monitor the physiological status of the ribosome (and/or DNA replication) and then control the initiation of sporulation via the phosphorelay pathway, as well as regulating the assembly of the ribosome in order to provide sufficient amounts of active ribosomes in sporulating cells.…”

A Role for Nonessential Domain II of Initiator Protein, DnaA, in Replication Control

“…Our genetic analysis also identified ObgE as a function required for survival of replication inhibition and suggested that ObgE may control replication fork stability, chromosome organization, or segregation (Foti et al 2005(Foti et al , 2007. Viable hypomorphic mutants in obgE were synthetically lethal with those negating doublestrand break repair (Foti et al 2005) and have modest over-replication and asynchronous replication phenotypes.…”

Functional Analysis of the Essential GTP-Binding-Protein-Coding GenecgtAofVibrio cholerae

“…Foti et al (7) isolated an obgE mutant that was sensitive to various replication inhibitors, like hydroxyurea (HU). Further studies by the same group showed that ObgE is required for cell cycle progression in E. coli (8). Sato et al (25) recently showed that ObgE is associated with several ribosomal proteins.…”

“…To demonstrate the essentiality of cgtA in the V. cholerae ⌬relA strain, we performed similar spot dilution assays, and the results corroborated the results obtained with V. cholerae strain NcgtA13 (data not shown). It should be mentioned that very recently two different groups working on the stringent response and cgtA gene function of E. coli failed to isolate an E. coli ⌬cgtA ⌬relA double mutant (8,13). Altogether, it appears that the cgtA gene is essential in a relA mutant background in both V. cholerae and E. coli.…”

“…The GTP-binding protein CgtA, coded by the cgtA gene, belonging to Obg subfamily has been found to be highly conserved and essential in prokaryotes (14,15,17,20,22,23,27). Studies conducted with different prokaryotic organisms have suggested functional roles of the CgtA/Obg protein in various physiological processes, like regulation of initiation of sporulation (30), DNA replication (15,26), chromosome partitioning (14), replication fork stability (7), chromosome segregation (8), ribosome maturation (12,25), and maintaining the steady-state level of ppGpp during exponential growth (13). It has been demonstrated that Escherichia coli temperature-sensitive obgE (cgtA) mutant cells form long filaments with expanded, nonpartitioned chromosomes (14).…”