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Related Concept Videos

Conservative Site-specific Recombination and Phase Variation02:53

Conservative Site-specific Recombination and Phase Variation

Because the DNA segments are cut and reorganized in a direction-specific manner, site-specific recombination has emerged as an efficient genetic engineering technique. Flippase and Cyclization recombinases or Flp and Cre, respectively, are two members of the tyrosine recombinase family derived from bacteriophages, that are used to mediate site-specific DNA insertions, deletions, and targeted expression of proteins in mammalian cell lines.
The recognition sites for Cre recombinase called LoxP...
Exon Recombination02:32

Exon Recombination

The evolution of new genes is critical for speciation. Exon recombination, also known as exon shuffling or domain shuffling, is an important means of new gene formation. It is observed across vertebrates, invertebrates, and in some plants such as potatoes and sunflowers. During exon recombination, exons from the same or different genes recombine and produce new exon-intron combinations, which might evolve into new genes. 
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CRISPR and crRNAs02:53

CRISPR and crRNAs

Bacteria and archaea are susceptible to viral infections just like eukaryotes; therefore, they have developed a unique adaptive immune system to protect themselves. Clustered regularly interspaced short palindromic repeats and CRISPR-associated proteins (CRISPR-Cas) are present in more than 45% of known bacteria and 90% of known archaea.
The CRISPR-Cas system stores a copy of foreign DNA in the host genome and uses it to identify the foreign DNA upon reinfection. CRISPR-Cas has three different...
Homologous Recombination02:31

Homologous Recombination

The basic reaction of homologous recombination (HR) involves two chromatids that contain DNA sequences sharing a significant stretch of identity. One of these sequences uses a strand from another as a template to synthesize DNA in an enzyme-catalyzed reaction. The final product is a novel amalgamation of the two substrates. To ensure an accurate recombination of sequences, HR is restricted to the S and G2 phases of the cell cycle. At these stages, the DNA has been replicated already and the...
Homologous Recombination02:31

Homologous Recombination

The basic reaction of homologous recombination (HR) involves two chromatids that contain DNA sequences sharing a significant stretch of identity. One of these sequences uses a strand from another as a template to synthesize DNA in an enzyme-catalyzed reaction. The final product is a novel amalgamation of the two substrates. To ensure an accurate recombination of sequences, HR is restricted to the S and G2 phases of the cell cycle. At these stages, the DNA has been replicated already and the...
Gene Conversion02:08

Gene Conversion

Other than maintaining genome stability via DNA repair, homologous recombination plays an important role in diversifying the genome. In fact, the recombination of sequences forms the molecular basis of genomic evolution. Random and non-random permutations of genomic sequences create a library of new amalgamated sequences. These newly formed genomes can determine the fitness and survival of cells. In bacteria, homologous and non-homologous types of recombination lead to the evolution of new...

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Preparation of the Mgm101 Recombination Protein by MBP-based Tagging Strategy
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Published on: June 25, 2013

The dif/Xer recombination systems in proteobacteria.

Christophe Carnoy1, Claude-Alain Roten

  • 1INSERM U801, Lille, France. christophe.carnoy@univ-lille2.fr

Plos One
|September 4, 2009
PubMed
Summary

The dif/Xer system, crucial for resolving bacterial chromosome dimers, is widespread in proteobacteria, though variations exist. Some pathogenic epsilon-proteobacteria utilize a distinct XerH recombinase system, while others lack dif/Xer homologs.

Area of Science:

  • Bacteriology
  • Molecular Biology
  • Genomics

Background:

  • Bacterial DNA replication can produce dimeric chromosomes, requiring resolution by specific recombinase systems.
  • The dif/Xer system, involving XerC and XerD recombinases targeting the dif motif, is known in E. coli.
  • Alternative XerS/dif(SL) systems exist in streptococci and lactococci, suggesting diverse chromosomal resolution mechanisms.

Purpose of the Study:

  • To extensively characterize the dif/Xer system within the Proteobacteria phylum, a major group of sequenced bacterial genomes.
  • To identify the prevalence and characteristics of dif/XerCD and alternative recombination systems in Proteobacteria.
  • To investigate the presence of chromosomal deconcatenation systems in bacteria lacking dif/Xer homologs.

Main Methods:

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Determination of the Optimal Chromosomal Location(s) for a DNA Element in Escherichia coli Using a Novel Transposon-mediated Approach
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Determination of the Optimal Chromosomal Location(s) for a DNA Element in Escherichia coli Using a Novel Transposon-mediated Approach
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  • Bioinformatic analysis of 234 chromosomes from 156 proteobacterial species.
  • Identification and characterization of XerC, XerD, and related dif sequences.
  • Phylogenetic analysis of recombinases and comparative analysis of motif structures.

    • Main Results:

    • 87.8% of analyzed proteobacteria harbor XerC/XerD-like recombinases and dif-related sequences with specific characteristics (non-coding, near terminus, palindromic, low G+C, conserved XerD site).
    • A subgroup of pathogenic epsilon-proteobacteria (e.g., Helicobacter, Campylobacter) possesses a distinct XerH recombinase and dif(H) motif.
    • No dif or Xer homologs were found in small endosymbiont genomes or certain larger-chromosome bacteria (e.g., Legionellales).

    Conclusions:

    • The dif/XerCD system is prevalent in Proteobacteria, but significant variations and alternative systems exist.
    • The discovery of the XerH system in epsilon-proteobacteria highlights the diversity of bacterial chromosome resolution.
    • The absence of dif/Xer homologs in some species suggests the presence of alternative, yet undiscovered, deconcatenation mechanisms.