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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...
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The double-stranded structure of DNA has two major advantages. First, it serves as a safe repository of genetic information where one strand serves as the back-up in case the other strand is damaged. Second, the double-helical structure can be wrapped around proteins called histones to form nucleosomes, which can then be tightly wound to form chromosomes. This way, DNA chains up to 2 inches long can be contained within microscopic structures in a cell. A double-stranded break not only damages...
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Translesion (TLS) polymerases rescue stalled DNA polymerases at sites of damaged bases by replacing the replicative polymerase and installing a nucleotide across the damaged site. Doing so, TLS allows additional time for the cell to repair the damage before resuming regular DNA replication.
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LTR retrotransposons are class I transposable elements with long terminal repeats flanking an internal coding region. These elements are less abundant in mammals compared to other class I transposable elements. About 8 percent of human genomic DNA comprises LTR retrotransposons. Some of the common examples of LTR retrotransposons are Ty elements in yeast and Copia elements in Drosophila.
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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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Visualization of DNA Repair Proteins Interaction by Immunofluorescence
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Group II intron-like reverse transcriptases function in double-strand break repair.

Seung Kuk Park1, Georg Mohr1, Jun Yao1

  • 1Departments of Molecular Biosciences and Oncology, University of Texas at Austin, Austin, TX 78712, USA.

Cell
|September 16, 2022
PubMed
Summary
This summary is machine-generated.

Bacteria possess reverse transcriptases (RTs) that function in DNA repair. These enzymes perform translesion DNA synthesis and double-strand break repair (DSBR) through microhomology-mediated end-joining (MMEJ).

Keywords:
Alt-EJDNA repair polymerasealternative end joininghigh-throughput sequencinginsect R2 elementnon-retroviral reverse transcriptasetargetronthermostable group II intron reverse transcriptase

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Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • Bacteria encode reverse transcriptases (RTs) structurally related to group II intron RTs, with largely unknown functions.
  • Group II intron RTs are known mobile genetic elements involved in RNA splicing and retrohoming.

Purpose of the Study:

  • To investigate the function of a group II intron-like RT (G2L4 RT) from Pseudomonas aeruginosa.
  • To determine if bacterial RTs can function in DNA repair pathways, specifically translesion DNA synthesis and double-strand break repair (DSBR).

Main Methods:

  • Biochemical characterization of G2L4 RT.
  • Expression of G2L4 RT in Escherichia coli.
  • Site-directed mutagenesis to analyze active site residues (YIDD vs. YADD).
  • Comparative analysis with human DNA repair polymerase theta and other non-LTR retroelement RTs.

Main Results:

  • G2L4 RT, with a YIDD active site, exhibits DNA repair activities in its native host and in E. coli.
  • G2L4 RT performs translesion DNA synthesis and DSBR via microhomology-mediated end-joining (MMEJ).
  • Its biochemical activities are similar to human DNA repair polymerase theta.
  • Reciprocal active-site substitutions revealed isoleucine favors MMEJ and alanine favors primer extension in both group II intron RT and G2L4 RT.

Conclusions:

  • Bacterial group II intron-like RTs possess inherent DNA repair capabilities, including DSBR.
  • These functions rely on conserved structural features shared with eukaryotic non-LTR retroelement RTs.
  • Bacterial RTs may play a conserved role in DSBR across diverse organisms.