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At least 109 records · Page 6Linked to original sources
PubMed1984

Replication control of IncP plasmids.

Clones of Escherichia coli with a chromosomally integrated RP4-prime plasmid were isolated and characterized. Chromosome transfer was increased about 50-fold and the Hfr still carried an autonomous plasmid indistinguishable from the original RP4-prime. This could be eliminated by pRP64 or R751, two distinguishably marked incompatible plasmids, giving rise to strains which stably retained the resistance patterns of both plasmids and which continued to transfer the chromosome at enhanced levels. In both cases, however, the copy number of the autonomous plasmid was reduced by the presence of a chromosomal RP4 such that the total number of P plasmid genomes (integrated and autonomous) remained constant. The results are consistent with the idea that copy number is controlled by diffusible inhibitors or initiators of replication.

Chromosomes, Bacterial↗
PubMed2001

[Chromosome replication in mycobacteria].

Variation in growth rate has provided a basis for the broad classification of Mycobacterium: (i) the slow-growing class includes the human pathogens Mycobacterium tuberculosis and M. leprae, and (ii) the fast-growing class includes saprophytic nonpathogens, such as M. smegmatis. An intimate association between DNA chromosomal replication and growth rate have been suggested. However, the molecular basis of this relation is unknown. In this article, we summarise our recent work on the study of the origin replication region of some species of mycobacteria, determination of the factors regulating the initiation of DNA replication and the characterisation of the main factor of the replicative machinery, the DnaA protein.

Bacterial Proteins↗
PubMed1998

A fixed distance for separation of newly replicated copies of oriC in Bacillus subtilis: implications for co-ordination of chromosome segregation and cell division.

The Spo0J protein of Bacillus subtilis is required for normal chromosome segregation and forms discrete subcellular assemblies closely associated with the oriC region of the chromosome. Here we show that duplication of Spo0J foci occurs early in the DNA replication cycle and that this requires the initiation of DNA replication at oriC but not elongation beyond the nearby STer sites. Soon after duplication, sister oriC/Spo0J foci move rapidly apart to achieve a fixed separation of about 0.7 microm, reminiscent of the segregation of eukaryotic chromosomes on the mitotic spindle. The magnitude of the fixed separation distance may explain how chromosome segregation is kept in close register with cell growth and the initiation mass for DNA replication. It could also explain how segregation can proceed accurately in the absence of cell division. The kinetics of focal separation suggest that one role of Spo0J protein may be to facilitate formation of separate sister oriC complexes that can be segregated.

Bacillus subtilis↗
PubMed1989

[Dependence of the recA gene for the replication of the bacterial chromosome initiated by the integrated F' plasmid in Escherichia coli].

Mutant strain dnaA46 of Escherichia coli can be integratively suppressed by the F' plasmid. Upon introducing the recA56 mutation through transduction the suppressive integration strain (Sin) becomes unable to grow at 40 degrees C. By means of experiments of marker transfer, acridine orange sensitivity test, F' curing and mini-chromosome transformation it is concluded that the F' plasmid is always in an integrated state in the Sin strains and that the initiation of the replication of the bacterial chromosome is carried on by the integrated F' plasmid. The biosynthesis of DNA and protein of the Sin recA+ and Sin recA- strains at different temperatures were compared. It is concluded from the experimental results that the recA gene functions at the level of DNA replication. The recA gene is known to be the key gene in DNA recombination and SOS repair of DNA damage. The works reported here throw some light on the understanding of the function of the recA gene.

Chromosomes, Bacterial↗
PubMed1993

Three distinct chromosome replication states are induced by increasing concentrations of DnaA protein in Escherichia coli.

The DnaA protein concentration in Escherichia coli was increased above the wild-type level by inducing a lacP-controlled dnaA gene located on a plasmid. In these cells with different DnaA protein levels, we measured several parameters: dnaA gene expression; cell size, amount of DNA per cell, and number of origins per cell by flow cytometry; and origin-to-terminus ratio and the frequencies of five other markers on the chromosome by Southern hybridization. The response of the cells to higher levels of DnaA protein could be divided into three states. From the normal level to a level 1.5-fold higher, DnaA protein had little effect on dnaA gene expression and the rate of DNA replication but led to nearly proportional increases in DNA and origin concentrations. Between 1.5- and 3-fold, the normal DnaA protein concentration, dnaA gene expression was gradually decreased. In this interval, the origin concentration increased significantly; however, the replication rate was severely affected, becoming slower--especially near the origin--the higher the DnaA protein concentration, and as a result, the DNA concentration was constant. Further increases in the DnaA protein concentration did not lead to an increased origin concentration. Thus, the initiation mass was set by the DnaA protein from the normal level to an at least twofold-increased level, but the increased initiation did not lead to a large increase in the amount of DNA per unit of mass because of the inhibition of replication fork velocity.

Bacterial Proteins↗
PubMedDate not supplied

DNA segregation: putting chromosomes in their place.

Recent studies provide evidence that bacterial chromosomes are replicated by an enzyme factory, the replisome, located at a fixed position at the center of the cell; the fixed replisome could be a major factor in determining chromosome order in the cell, and may provide the force that drives chromosome segregation.

Bacteria↗
PubMed1987

Evidence for the involvement of the 16kD gene promoter in initiation of chromosomal replication of Escherichia coli strains carrying a B/r-derived replication origin.

Initiation of chromosomal DNA replication of several Escherichia coli dnaA (Ts) strains is diminished in cell harbouring pBR322 hybrid plasmids carrying both oriC and the adjacent 16kD gene promoter of E. coli K12. This perturbance, resulting in very slow growth, is caused both by the dnaA allele and the E. coli B/r-derived region of the replication origin of these strains. Cloning and DNA sequence analysis of the E. coli B/r replication origin revealed several base differences as compared to the E. coli K12 sequence. The replication origin of temperature sensitive fast growing mutants, originating from a homologous exchange between chromosomal and plasmid DNA sequences were also cloned. Sequence data showed that a single base change within the promoter of the 16kD gene of these dnaA (Ts) strains is able to suppress the inhibition of chromosomal DNA replication by the mentioned pBR322 hybrid plasmids. Our results strongly indicate a role of the 16kD gene promoter in control of initiation of chromosomal DNA replication.

Alleles↗
PubMed1970

6-(p-hydroxyphenylazo)-uracil: a selective inhibitor of host DNA replication in phage-infected Bacillus subtilis.

The azopyrimidine, 6-(p-hydroxyphenylazo)-uracil, inhibits the replication of bacterial DNA selectively, completely, and reversibly, and has no apparent effects on the metabolism of other cellular macromolecules thus far examined. The mechanism of its action has been investigated in uninfected and phage-infected Bacillus subtilis, and the compound appears to be specific for a host function. In cells infected with virulent phage the synthesis of phage DNA proceeds normally, while residual host DNA synthesis is completely blocked. The drug-sensitive host site retains its sensitivity even after partial disruption of the cell by lysozyme treatment.

Azo Compounds↗
PubMed1991

The replication termination signal terB of the Escherichia coli chromosome is a deletion hot spot.

Hybrids composed of phage M13, plasmid pBR322 and the termination signal of Escherichia coli chromosome replication terB were used to show that arrest of DNA synthesis creates a very efficient deletion hot spot. Up to 80% of deletions occurring in these hybrids had one deletion end-point at terB provided that (i) terB was oriented to arrest M13 and pBR322 leading strand synthesis; and (ii) the host cells contained the Tus protein necessary for arresting DNA synthesis at terB. The position of terB and the flanking sequences had little effect on deletion hot spot activity. About 90% of the deletions at terB ended 5-6 nucleotides in front of the major replication arrest site. We propose two models to account for deletion formation and speculate that many genome rearrangements may be due to the pausing of DNA replication.

Base Sequence↗
PubMed1978

Identification of a biochemically unique DNA-membrane interaction involving the Escherichia coli origin of replication.

DNA-membrane complexes have been obtained from Escherichia coli by using a freeze-thaw lysis procedure that avoids lysozyme and detergents. Complexes made in this manner and containing DNA near the origin of replication are uniquely sensitive to ionic strength, Pronase, and trypsin. There is approximately one such complex per chromosomal origin. The sensitivities suggest that origin-specific binding is mediated by a protein. By using these unique characteristics to distinguish origin-specific complexes from the majority of DNA-membrane binding sites, it was found that the origin-specific binding persists after termination of chromosomal replication.

Cell Membrane↗