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At least 127 records · Page 7Linked to original sources
PubMed1991

Experiments on chromosome separation and positioning in Escherichia coli.

The way in which sister genomes are spatially separated after replication and positioned in sister cells after division remains unknown for prokaryotes. Experiments with Escherichia coli suggest that individual "chromosomes" (folded, covalently closed circular DNA molecules) are fixed in position within growing cells both before and during replication, but that they are rapidly moved apart by a fixed distance (unit length) immediately after replication has been completed. Such a mitosis-like mechanism accounts for the aberrant positions of DNA and septa in cells in which the normal coordination between DNA replication and cell elongation has been perturbed.

Cell Division↗
PubMed2003

Bacterial chromosome dynamics.

Bacterial chromosomes are highly compacted structures and share many properties with their eukaryote counterparts, despite not being organized into chromatin or being contained within a cell nucleus. Proteins conserved across all branches of life act in chromosome organization, and common mechanisms maintain genome integrity and ensure faithful replication. The principles that underlie chromosome segregation in bacteria and eukaryotes share similarities, although bacteria segregate DNA as it replicates and lack a eukaryote-like mitotic apparatus for segregating chromosomes. This may be because the distances that newly replicated bacterial chromosomes move apart before cell division are small as compared to those in eukaryotes. Bacteria specify positional information, which determines where cell division will occur and which places the replication machinery and chromosomal loci at defined locations that change during cell cycle progression.

Bacterial Physiological Phenomena↗
PubMed1978

Organization and expression of the dnaJ and dnaK genes of Escherichia coli K12.

A temperature-sensitive mutation in the dnaJ gene of Escherichia coli K12 is described which affects replication of the bacterial DNA. The gene is located adjacent to the dnaK gene described previously (Saito and Uchida, 1977). The physical and functional organization of the dnaJ-dnaK region was studied in detail by analyzing the heteroduplexes and functions of various deletion mutants of lambdadnaJdnaK, a transducing phage carrying both of the dna genes. The sizes of dnaJ and dnaK cistrons were estimated to be at most 1.2 +/- 0.5 and 2.1 +/- 0.4 kilobases, respectively. In vivo expression of the dnaJ function by various deletion phages indicated that the dnaK and dnaJ cistrons were transcribed from a promoter located at the head of the dnaK cistron, dnaJ being downstream to dnaK. Presence of a weak promoter which reads only the dnaJ cistron was also suggested. A simple method for isolating independent deletion mutants of phage lambda was described.

Chromosome Mapping↗
PubMed2005

Deletion of the datA site does not affect once-per-cell-cycle timing but induces rifampin-resistant replication.

In Escherichia coli, three mechanisms have been proposed to maintain proper regulation of replication so that initiation occurs once, and only once, per cell cycle. First, newly formed origins are inactivated by sequestration; second, the initiator, DnaA, is inactivated by the Hda protein at active replication forks; and third, the level of free DnaA protein is reduced by replication of the datA site. The datA site titrates unusually large amounts of DnaA and it has been reported that reinitiation, and thus asynchrony of replication, occurs in cells lacking this site. Here, we show that reinitiation in deltadatA cells does not occur during exponential growth and that an apparent asynchrony phenotype results from the occurrence of rifampin-resistant initiations. This shows that the datA site is not required to prevent reinitiation and limit initiation of replication to once per generation. The datA site may, however, play a role in timing of initiation relative to cell growth. Inactivation of active ATP-DnaA by the Hda protein and the sliding clamp of the polymerase was found to be required to prevent reinitiation and asynchrony of replication.

Adenosine Triphosphatases↗
PubMed1985

DNA-protein interactions during replication of genetic elements of bacteria.

Specific interactions of DNA with proteins are required for both the replication of deoxyribonucleic acid proper and its regulation. Genetic elements of bacteria, their extrachromosomal elements in particular, represent a suitable model system for studies of these processes at the molecular level. In addition to replication enzymes (DNA polymerases), a series of other protein factors (e.g. topoisomerases, DNA unwinding enzymes, and DNA binding proteins) are involved in the replication of the chromosomal, phage and plasmid DNA. Specific interactions of proteins with DNA are particularly important in the regulation of initiation of DNA synthesis. Association of DNAs with the cell membrane also plays an important role in their replication in bacteria.

Bacterial Proteins↗
PubMed2000

DNA segregation in bacteria.

Segregation of DNA in bacterial cells is an efficient process that assures that every daughter cell receives a copy of genomic and plasmid DNA. In this review, we focus primarily on observations in recent years, including the visualization of DNA and proteins at the subcellular level, that have begun to define the events that separate DNA molecules. Unlike the process of chromosome segregation in higher cells, segregation of the bacterial chromosome is a continuous process in which chromosomes are separated as they are replicated. Essential to separation is the initial movement of sister origins to opposite ends of the cell. Subsequent replication and controlled condensation of DNA are the driving forces that move sister chromosomes toward their respective origins, which establishes the polarity required for segregation. Final steps in the resolution and separation of sister chromosomes occur at the replication terminus, which is localized at the cell center. In contrast to the chromosome, segregation of low-copy plasmids, such as Escherichia coli F, P1, and R1, is by mechanisms that resemble those used in eukaryotic cells. Each plasmid has a centromere-like site to which plasmid-specified partition proteins bind to promote segregation. Replication of plasmid DNA, which occurs at the cell center, is followed by rapid partition protein-mediated separation of sister plasmids, which become localized at distinct sites on either side of the division plane. The fundamental similarity between chromosome and plasmid segregation-placement of DNA to specific cell sites-implies an underlying cellular architecture to which both DNA and proteins refer.

Cell Compartmentation↗
PubMed1972

Deoxyribonucleic acid replication and cell division in Escherichia coli at 33 C.

At 33 C (60-min generation time) the time required to replicate the chromosome is C = 60 min. The time between the end of a round of replication and cell division is D = 20 min, as at 37 C. Nalidixic acid and a temperature shift in a dnaB mutant give identical results for the determination of the end of a round of replication.

Cell Division↗
PubMed1989

Staphylococcus aureus chromosomal mutations that decrease efficiency of Rep utilization in replication of pT181 and related plasmids.

Staphylococcus aureus chromosomal mutants which maintain pT181 and related plasmids at a much reduced copy number but which do not affect the replication of other plasmids have been isolated. The origin of replication and the initiator protein of the affected plasmids are the only elements required for the response to these mutations. The host mutations do not interfere with the pT181 replication control mechanism.

Chromosomes, Bacterial↗
PubMed2006

Spo0A, the key transcriptional regulator for entrance into sporulation, is an inhibitor of DNA replication.

The transcription factor Spo0A is a master regulator for entry into sporulation in Bacillus subtilis and also regulates expression of the virulent B. subtilis phage phi29. Here, we describe a novel function for Spo0A, being an inhibitor of DNA replication of both, the phi29 genome and the B. subtilis chromosome. Binding of Spo0A near the phi29 DNA ends, constituting the two origins of replication of the linear phi29 genome, prevents formation of phi29 protein p6-nucleoprotein initiation complex resulting in inhibition of phi29 DNA replication. At the B. subtilis oriC, binding of Spo0A to specific sequences, which mostly coincide with DnaA-binding sites, prevents open complex formation. Thus, by binding to the origins of replication, Spo0A prevents the initiation step of DNA replication of either genome. The implications of this novel role of Spo0A for phage phi29 development and the bacterial chromosome replication during the onset of sporulation are discussed.

Bacillus Phages↗
PubMed2000

Rifampicin-resistant initiation of chromosome replication from oriC in ihf mutants.

IHF (integration host factor) mutants exhibit asynchronous initiation of chromosome replication from oriC as determined from flow cytometric analysis of cultures where RNA synthesis was inhibited with rifampicin. However, the run-out kinetics of chromosome replication in ihf mutants shows that they continue to produce oriCs for some time in the absence of RNA synthesis resulting in a twofold increase in the oriC per mass ratio. An ihf dnaA double mutant did not exhibit this continued increase of the oriC per mass ratio. This indicates that ihf mutants can initiate replication from oriC in a rifampicin-resistant initiation mode but requires fully functional DnaA protein. The origin per mass ratio, determined by a quantitative Southern blotting technique, showed that the ihf mutants had an origin per mass ratio that was 60% of the wild type although it had a normal DnaA protein concentration. This shows that the initiation mass was substantially higher in the ihf mutants. The oriC per terminus ratio, which was also determined by Southern blotting, was very low in the ihf mutant, although it grew with the same doubling times as the wild-type strain. This indicates that cells lacking IHF replicate their chromosome(s) very fast.

Bacterial Proteins↗
PubMed2003

Identification and characterization of a pSLA2 plasmid locus required for linear DNA replication and circular plasmid stable inheritance in Streptomyces lividans.

Streptomyces linear plasmids and linear chromosomes can replicate also in a circular form when their telomeres are deleted. The 17-kb linear plasmid pSLA2 has been a useful model in studies of such replicons. Here we report that the minimal origin initiating replication of pSLA2-derived plasmids as circular molecules cannot propagate these plasmids in a linear mode unless they also contain a novel plasmid-encoded locus, here named rlrA (required for linear replication). In contrast with the need for rlrA to accomplish replication of telomere-containing linear plasmids, expression of rlrA, which encodes two LuxR family regulatory domains, interferes with the establishment of pSLA2 in circular form in Streptomyces lividans transformants. The additional presence of an adjacent divergently transcribed locus, rorA (rlrA override), which strongly resembles the kor (kil override) transcription control genes identified previously on Streptomyces plasmids, reversed the detrimental effects of rlrA on plasmid establishment and additionally stabilized circular plasmid inheritance by spores during the S. lividans life cycle. While the effects of the rlrA/rorA locus of pSLA2 were seen also on linear plasmids derived from the unrelated SLP2 replicon, they did not extend to plasmids whose replication was initiated at a cloned chromosomal origin. Our results establish the existence of, and provide the initial description of, a novel plasmid-borne regulatory system that differentially affects the propagation of linear and circular plasmids in Streptomyces.

Amino Acid Sequence↗
PubMed1990

Loss of DNA-membrane interactions and cessation of DNA synthesis in myeloperoxidase-treated Escherichia coli.

Neutrophils and monocytes employ a diverse array of antimicrobial effector systems to support their host defense functions. The mechanisms of action of most of these systems are incompletely understood. The present report indicates that microbicidal activity by a neutrophil-derived antimicrobial system, consisting of myeloperoxidase, enzymatically generated hydrogen peroxide, and chloride ion, is accompanied by prompt cessation of DNA synthesis in Escherichia coli, as determined by markedly reduced incorporation of [3H]thymidine into trichloracetic acid-precipitable material. Simultaneously, the myeloperoxidase system mediates a decline in the ability of E. coli membranes to bind hemimethylated DNA sequences containing the E. coli chromosomal origin of replication (oriC). Binding of oriC to the E. coli membrane is an essential element of orderly chromosomal DNA replication. Comparable early changes in DNA synthesis and DNA-membrane interactions were not observed with alternative oxidant or antibiotic-mediated microbicidal systems. It is proposed that oxidants generated by the myeloperoxidase system modify the E. coli membrane in such a fashion that oriC binding is markedly impaired. As a consequence chromosomal DNA replication is impaired and organisms can no longer replicate.

Cell Membrane↗