MreB Actin-Mediated Segregation of a Specific Region of a Bacterial Chromosome

Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States
Cell (Impact Factor: 32.24). 03/2005; 120(3):329-41. DOI: 10.1016/j.cell.2005.01.007
Source: PubMed


Faithful chromosome segregation is an essential component of cell division in all organisms. The eukaryotic mitotic machinery uses the cytoskeleton to move specific chromosomal regions. To investigate the potential role of the actin-like MreB protein in bacterial chromosome segregation, we first demonstrate that MreB is the direct target of the small molecule A22. We then demonstrate that A22 completely blocks the movement of newly replicated loci near the origin of replication but has no qualitative or quantitative effect on the segregation of other loci if added after origin segregation. MreB selectively interacts, directly or indirectly, with origin-proximal regions of the chromosome, arguing that the origin-proximal region segregates via an MreB-dependent mechanism not used by the rest of the chromosome.

Full-text preview

Available from:
  • Source
    • "These investigations have revealed that higher-order spatial organization, once thought to be a property specific to eukaryotic cells, are also important characteristics of bacterial cells (Gitai et al., 2005; Shapiro et al., 2009). This organization can be highly dynamic over time, and an astonishing array of different spatiotemporal protein localization patterns has been uncovered ranging from proteins with a relatively stationary localization, proteins with dynamic localization and changing localization in a cell cycle-dependent or cell cycle-independent manner, proteins forming gradients, to proteins that oscillate rapidly over the chromosome or between the cell poles. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Many bacterial proteins involved in fundamental processes such as cell shape maintenance, cell cycle regulation, differentiation, division and motility localize dynamically to specific subcellular regions. However, the mechanisms underlying dynamic protein localization are incompletely understood. Using the SpoIIQ protein in Bacillus subtilis as a case study, two reports in this issue of Molecular Microbiology present important novel insights into how a protein finds its right place at the right time and remains stably bound. During sporulation, SpoIIQ localizes in clusters in the forespore membrane at the interface that separates the forespore and mother cell and functions as a landmark protein for SpoIIIAH in the mother cell membrane. The extracellular domains of SpoIIQ and SpoIIIAH interact directly effectively bridging the gap between the two membranes. Here, SpoIIQ localization is shown to depend on two pathways, one involves SpoIIIAH, the second involves two peptidoglycan degrading enzymes SpoIIP and SpoIID; and, SpoIIQ is only delocalized in the absence of all three proteins. Importantly, in the absence of SpoIIIAH, SpoIIQ apparently localizes normally. However, FRAP experiments demonstrated that SpoIIQ is not stably maintained in the clusters in this mutant. Thus, a second targeting pathway can mask significant changes in the localization of a protein.
    Full-text · Article · Aug 2013 · Molecular Microbiology
  • Source
    • "Bacterial actins may also have roles in DNA replication. For instance, MreB, the bacterial actin homolog, was shown to mediate chromosome segregation [71] and regulate DNA Topoisomerase (Topo) IV activity; in the latter case, polymeric MreB stimulated while monomeric MreB inhibited Topo IV activity [72]. Certain eukaryote cytoskeletal proteins have been found in the nucleus and to associate with DNA replication machinery and mediate progression through S phase. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Actin, a constituent of the cytoskeleton, is now recognized to function in the nucleus in gene transcription, chromatin remodeling and DNA replication/repair. Actin shuttles in and out of the nucleus through the action of transport receptors importin-9 and exportin-6. Here we have addressed the impact of cell cycle progression and DNA replication stress on actin nuclear localization, through study of actin dynamics in living cells. First, we showed that thymidine-induced G1/S phase cell cycle arrest increased the nuclear levels of actin and of two factors that stimulate actin polymerization: IQGAP1 and Rac1 GTPase. When cells were exposed to hydroxyurea to induce DNA replication stress, the nuclear localization of actin and its regulators was further enhanced. We employed live cell photobleaching (FRAP) assays and discovered that in response to DNA replication stress, GFP-actin nuclear import and export rates increased by up to 250%. The rate of import was twice as fast as export, accounting for actin nuclear accumulation. The faster shuttling dynamics correlated with reduced cellular retention of actin, and our data implicate actin polymerization in the stress-dependent uptake of nuclear actin. Furthermore, DNA replication stress induced a nuclear shift in IQGAP1 and Rac1 with enhanced import dynamics. Proximity ligation assays revealed that IQGAP1 associates in the nucleus with actin and Rac1, and formation of these complexes increased after hydroxyurea treatment. We propose that the replication stress checkpoint triggers co-ordinated nuclear entry and trafficking of actin, and of factors that regulate actin polymerization.
    Full-text · Article · Jun 2013 · Biochimica et Biophysica Acta
  • Source
    • "Such a system is lacking in E. coli. The discovery of the protein filaments forming a bacterial cytoskeleton (for recent review, (Ingerson-Mahar and Gitai, 2012) and evidence suggesting that MreB contributes to the segregation of the origin of replication in C. crescentus (Gitai et al., 2005) suggested that the cytoskeleton might play an important role in the segregation of the chromosome in rod/crescent shape bacteria. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The mechanisms driving bacterial chromosome segregation remain poorly characterized. While a number of factors influencing chromosome segregation have been described in recent years, none of them appeared to play an essential role in the process comparable to the eukaryotic centromere / spindle complex. The research community involved in bacterial chromosome was becoming familiar with the fact that bacteria have selected multiple redundant systems to ensure correct chromosome segregation. Over the past few years a new perspective came out, that entropic forces generated by the confinement of the chromosome in the crowded nucleoid shell could be sufficient to segregate the chromosome. The segregating factors would only be required to create adequate conditions for entropy to do its job. In the article by Yazdi and collaborators, in this issue of Molecular Microbiology, this model was challenged experimentally in live E. coli cells. A Fis-GFP fusion was used to follow nucleoid choreography and analyze it from a polymer physics perspective. Their results suggest strongly that E. coli nucleoids behave as self-adherent polymers. Such a structuring and the specific segregation patterns observed do not support an entropic like segregation model. Are we back to the pre-entropic era ?
    Full-text · Article · Oct 2012 · Molecular Microbiology
Show more

We use cookies to give you the best possible experience on ResearchGate. Read our cookies policy to learn more.