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Related Concept Videos

Replication in Prokaryotes01:32

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DNA replication has three main steps: initiation, elongation, and termination. Replication in prokaryotes begins when initiator proteins bind to the single origin of replication (ori) on the cell's circular chromosome. Replication then proceeds around the entire circle of the chromosome in each direction from the two replication forks, resulting in two DNA molecules.
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DNA replication is carried out by a large complex of proteins that act in a coordinated matter to achieve high-fidelity DNA replication. Together this complex is known as the DNA replication machinery or the replisome.
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In eukaryotic cells, DNA replication is highly conserved and tightly regulated. Multiple linear chromosomes must be duplicated with high fidelity before cell division, so there are many proteins that fulfill specialized roles in the replication process. Replication occurs in three phases: initiation, elongation, and termination, and ends with two complete sets of chromosomes in the nucleus.
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Before a cell can divide, it must accurately replicate all of its chromosomes, including the DNA and its associated histone and non-histone proteins.  This process begins at numerous origins of replication during the S phase of the cell cycle in each of a cell’s chromosomes simultaneously. Certain nucleotides can act as origins of replication, but these sequences are not well defined - especially in complex, multi-cellular, eukaryotic species. The length of DNA that spans an origin...
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Determination of the Optimal Chromosomal Locations for a DNA Element in Escherichia coli Using a Novel Transposon-mediated Approach
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Evolutionary Changes in DnaA-Dependent Chromosomal Replication in Cyanobacteria.

Ryudo Ohbayashi1, Shunsuke Hirooka1, Ryo Onuma1

  • 1Department of Gene Function and Phenomics, National Institute of Genetics, Shizuoka, Japan.

Frontiers in Microbiology
|May 16, 2020
PubMed
Summary

Most bacteria use DnaA protein for DNA replication initiation. However, some cyanobacteria lack DnaA or use alternative replication methods, suggesting evolutionary flexibility in bacterial chromosome replication.

Keywords:
CDS skewDnaAGC skewchromosome replicationcyanobacteriapolyploidy

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Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • Bacterial chromosome replication typically initiates at a unique origin (oriC) in a DnaA-dependent manner.
  • GC skew profiles often reveal asymmetry between leading and lagging DNA strands in bacterial chromosomes.
  • The DnaA-oriC replication mechanism was considered essential for most bacteria, with no known free-living bacteria lacking the dnaA gene.

Purpose of the Study:

  • To investigate the diverse mechanisms of cyanobacterial chromosome replication.
  • To explore the prevalence and implications of DnaA-independent replication strategies in cyanobacteria.

Main Methods:

  • Comparative genomic analysis to identify the presence or absence of the dnaA gene.
  • Investigation of chromosome replication origins and mechanisms in various cyanobacterial species.
  • Phylogenetic analysis to understand evolutionary relationships and gene loss events.

Main Results:

  • Several free-living cyanobacteria, including Cyanobacterium aponinum PCC 10605 and Geminocystis sp. NIES-3708, lack the dnaA gene and utilize multiple replication origins.
  • Synechococcus sp. PCC 7002 possesses dnaA but replicates its chromosome from a unique origin independently of DnaA-oriC.
  • Loss of DnaA-oriC dependency appears to have occurred multiple times independently during cyanobacterial evolution, potentially correlating with increased ploidy.

Conclusions:

  • Cyanobacterial chromosome replication exhibits significant diversity, challenging the universality of the DnaA-oriC model.
  • The loss of dnaA or DnaA-oriC dependency represents an adaptive evolutionary strategy in certain cyanobacteria.
  • Further research is needed to fully understand the implications of these diverse replication mechanisms and their correlation with ploidy.