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Mutations in Microorganisms01:18

Mutations in Microorganisms

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Mutations are heritable changes in an organism’s genome involving alterations in the base sequence of DNA or RNA. These changes can influence cellular processes and phenotypic traits, potentially transforming the unaltered wild type into a mutant form. Such changes, termed forward mutations, are pivotal in shaping the genetic diversity of organisms.RNA viruses exhibit the highest mutation rates due to the absence of robust proofreading mechanisms during genome replication. In contrast,...
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Spontaneous and Induced Mutations01:30

Spontaneous and Induced Mutations

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Spontaneous mutations arise infrequently during DNA replication due to errors in the process. A key factor behind these errors is tautomeric shifts in nitrogenous bases, where bases transition from keto to enol forms or amino to imino forms. This shift can alter base-pairing rules, leading to mutations. Additionally, reactive oxygen species (ROS) arising from aerobic metabolism can damage DNA, resulting in depurination (loss of a purine base) or depyrimidination (loss of a pyrimidine base).
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Mismatch Repair01:20

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Organisms are capable of detecting and fixing nucleotide mismatches that occur during DNA replication. This sophisticated process requires identifying the new strand and replacing the erroneous bases with correct nucleotides. Mismatch repair is coordinated by many proteins in both prokaryotes and eukaryotes.
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Transduction01:16

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Among the three main modes of HGT—transformation, conjugation, and transduction—transduction is unique in that it is mediated by bacteriophages, or bacterial viruses.Transduction occurs in two ways. Generalized transduction occurs during the lytic cycle of a bacteriophage infection. In this process, bacteriophages infect bacterial cells, replicate within them, and ultimately cause cell lysis, releasing newly assembled virions. Occasionally, random fragments of the bacterial genome...
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Transfer RNA Synthesis

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One of the unique features of tRNA is the presence of modified bases. In some tRNAs, modified bases account for nearly 20% of the total bases in the molecule. Altogether, these unusual bases protect the tRNA from enzymatic degradation by RNases.
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Mutations01:39

Mutations

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GnT Motifs Can Increase T:A→G:C Mutation Rates Over 1000-fold in Bacteria.

James S Horton1,2, Joshua L Cherry3,4, Gretel Waugh2

  • 1Institut Cochin, Université Paris Cité, INSERM U1016, CNRS UMR 8104, Paris 75014, France.

Molecular Biology and Evolution
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Summary

Scientists identified a specific DNA sequence motif (GnT) that significantly increases mutation rates in bacteria, acting as a mutational hotspot. This finding helps predict and quantify mutation hotspots in genomes.

Keywords:
homopolymeric tractlocal nucleotide contextmutagenic nucleotide motifmutation hotspottransversion mutation

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Area of Science:

  • Genetics
  • Molecular Biology
  • Evolutionary Biology

Background:

  • Genomic mutation rates vary across nucleotide positions.
  • Specific sequences, known as mutational hotspots, exhibit elevated mutation frequencies.
  • Understanding the nucleotide sequences driving these hotspots is crucial for evolutionary studies.

Purpose of the Study:

  • To identify and characterize short nucleotide motifs responsible for high mutation rates.
  • To quantify the impact of flanking nucleotides on mutational hotspot activity.

Main Methods:

  • Experimental evolution in Pseudomonas fluorescens.
  • Bioinformatic analysis of Salmonella species genomes.
  • Characterization of a ≥8 bp nucleotide motif driving T:A→G:C mutations.

Main Results:

  • A GnT motif was identified, increasing T:A→G:C mutation rates over 1000-fold.
  • Homopolymeric guanine tracts (≥3) followed by a T (GnT) were confirmed as hotspots.
  • Mutation rate enhancement is dependent on nucleotides flanking the GnT sequence, with significant effects from 5' and 3' dinucleotides.

Conclusions:

  • The GnT motif, influenced by flanking nucleotides, acts as a potent bacterial mutational hotspot.
  • Mutation rate is modulated by modular nucleotide components within the hotspot motif.
  • This research improves the ability to identify and quantify mutation hotspots based on short DNA sequences.