scholarly journals DNA Double-Strand Breaks and Telomeres Play Important Roles in Trypanosoma brucei Antigenic Variation

2015 ◽  
Vol 14 (3) ◽  
pp. 196-205 ◽  
Author(s):  
Bibo Li
Keyword(s):  
Trypanosoma Brucei ◽  
Surface Antigen ◽  
Antigenic Variation ◽  
Dna Recombination ◽  
Double Strand Breaks ◽  
Microbial Pathogens ◽  
Dna Double Strand Breaks ◽  
Content Type ◽  
Strand Breaks ◽  
Major Surface

ABSTRACTHuman-infecting microbial pathogens all face a serious problem of elimination by the host immune response. Antigenic variation is an effective immune evasion mechanism where the pathogen regularly switches its major surface antigen. In many cases, the major surface antigen is encoded by genes from the same gene family, and its expression is strictly monoallelic. Among pathogens that undergo antigenic variation,Trypanosoma brucei(a kinetoplastid), which causes human African trypanosomiasis,Plasmodium falciparum(an apicomplexan), which causes malaria,Pneumocystis jirovecii(a fungus), which causes pneumonia, andBorrelia burgdorferi(a bacterium), which causes Lyme disease, also express their major surface antigens from loci next to the telomere. Except forPlasmodium, DNA recombination-mediated gene conversion is a major pathway for surface antigen switching in these pathogens. In the last decade, more sophisticated molecular and genetic tools have been developed inT. brucei, and our knowledge of functions of DNA recombination in antigenic variation has been greatly advanced. VSG is the major surface antigen inT. brucei. In subtelomeric VSG expression sites (ESs),VSGgenes invariably are flanked by a long stretch of upstream 70-bp repeats. Recent studies have shown that DNA double-strand breaks (DSBs), particularly those in 70-bp repeats in the active ES, are a natural potent trigger for antigenic variation inT. brucei. In addition, telomere proteins can influence VSG switching by reducing the DSB amount at subtelomeric regions. These findings will be summarized and their implications will be discussed in this review.

scholarly journals Genetic Separation of Sae2 Nuclease Activity from Mre11 Nuclease Functions in Budding Yeast

2017 ◽  
Vol 37 (24) ◽  
Author(s):  
Sucheta Arora ◽  
Rajashree A. Deshpande ◽  
Martin Budd ◽  
Judy Campbell ◽  
America Revere ◽  
...  
Keyword(s):  
Nuclease Activity ◽  
Double Strand Breaks ◽  
Endonuclease Activity ◽  
Dna Double Strand Breaks ◽  
Dna Breaks ◽  
Content Type ◽  
Strand Breaks ◽  
Dna Ends

ABSTRACT Sae2 promotes the repair of DNA double-strand breaks in Saccharomyces cerevisiae. The role of Sae2 is linked to the Mre11/Rad50/Xrs2 (MRX) complex, which is important for the processing of DNA ends into single-stranded substrates for homologous recombination. Sae2 has intrinsic endonuclease activity, but the role of this activity has not been assessed independently from its functions in promoting Mre11 nuclease activity. Here we identify and characterize separation-of-function mutants that lack intrinsic nuclease activity or the ability to promote Mre11 endonucleolytic activity. We find that the ability of Sae2 to promote MRX nuclease functions is important for DNA damage survival, particularly in the absence of Dna2 nuclease activity. In contrast, Sae2 nuclease activity is essential for DNA repair when the Mre11 nuclease is compromised. Resection of DNA breaks is impaired when either Sae2 activity is blocked, suggesting roles for both Mre11 and Sae2 nuclease activities in promoting the processing of DNA ends in vivo. Finally, both activities of Sae2 are important for sporulation, indicating that the processing of meiotic breaks requires both Mre11 and Sae2 nuclease activities.

scholarly journals Ku Heterodimer-Independent End Joining in Trypanosoma brucei Cell Extracts Relies upon Sequence Microhomology

2007 ◽  
Vol 6 (10) ◽  
pp. 1773-1781 ◽  
Author(s):  
Peter Burton ◽  
David J. McBride ◽  
Jonathan M. Wilkes ◽  
J. David Barry ◽  
Richard McCulloch
Keyword(s):  
Homologous Recombination ◽  
Trypanosoma Brucei ◽  
Antigenic Variation ◽  
Bacterial Species ◽  
Nonhomologous End Joining ◽  
Dna Double Strand Breaks ◽  
End Joining ◽  
Strand Breaks ◽  
Cell Extracts ◽  
Ligase Iv

ABSTRACT DNA double-strand breaks (DSBs) are repaired primarily by two distinct pathways: homologous recombination and nonhomologous end joining (NHEJ). NHEJ has been found in all eukaryotes examined to date and has been described recently for some bacterial species, illustrating its ancestry. Trypanosoma brucei is a divergent eukaryotic protist that evades host immunity by antigenic variation, a process in which homologous recombination plays a crucial function. While homologous recombination has been examined in some detail in T. brucei, little work has been done to examine what other DSB repair pathways the parasite utilizes. Here we show that T. brucei cell extracts support the end joining of linear DNA molecules. These reactions are independent of the Ku heterodimer, indicating that they are distinct from NHEJ, and are guided by sequence microhomology. We also demonstrate bioinformatically that T. brucei, in common with other kinetoplastids, does not encode recognizable homologues of DNA ligase IV or XRCC4, suggesting that NHEJ is either absent or mechanistically diverged in these pathogens.

scholarly journals Staphylococcal DNA Repair Is Required for Infection

mBio ◽  
2020 ◽  
Vol 11 (6) ◽  
Author(s):  
Kam Pou Ha ◽  
Rebecca S. Clarke ◽  
Gyu-Lee Kim ◽  
Jane L. Brittan ◽  
Jessica E. Rowley ◽  
...  
Keyword(s):  
Reactive Oxygen Species ◽  
Staphylococcus Aureus ◽  
Human Blood ◽  
Immune Cells ◽  
Double Strand Breaks ◽  
Oxygen Species ◽  
Dna Double Strand Breaks ◽  
Gram Positive ◽  
Content Type ◽  
Strand Breaks

ABSTRACT To cause infection, Staphylococcus aureus must withstand damage caused by host immune defenses. However, the mechanisms by which staphylococcal DNA is damaged and repaired during infection are poorly understood. Using a panel of transposon mutants, we identified the rexBA operon as being important for the survival of Staphylococcus aureus in whole human blood. Mutants lacking rexB were also attenuated for virulence in murine models of both systemic and skin infections. We then demonstrated that RexAB is a member of the AddAB family of helicase/nuclease complexes responsible for initiating the repair of DNA double-strand breaks. Using a fluorescent reporter system, we were able to show that neutrophils cause staphylococcal DNA double-strand breaks through reactive oxygen species (ROS) generated by the respiratory burst, which are repaired by RexAB, leading to the induction of the mutagenic SOS response. We found that RexAB homologues in Enterococcus faecalis and Streptococcus gordonii also promoted the survival of these pathogens in human blood, suggesting that DNA double-strand break repair is required for Gram-positive bacteria to survive in host tissues. Together, these data demonstrate that DNA is a target of host immune cells, leading to double-strand breaks, and that the repair of this damage by an AddAB-family enzyme enables the survival of Gram-positive pathogens during infection. IMPORTANCE To cause infection, bacteria must survive attack by the host immune system. For many bacteria, including the major human pathogen Staphylococcus aureus, the greatest threat is posed by neutrophils. These immune cells ingest the invading organisms and try to kill them with a cocktail of chemicals that includes reactive oxygen species (ROS). The ability of S. aureus to survive this attack is crucial for the progression of infection. However, it was not clear how the ROS damaged S. aureus and how the bacterium repaired this damage. In this work, we show that ROS cause breaks in the staphylococcal DNA, which must be repaired by a two-protein complex known as RexAB; otherwise, the bacterium is killed, and it cannot sustain infection. This provides information on the type of damage that neutrophils cause S. aureus and the mechanism by which this damage is repaired, enabling infection.

scholarly journals Critical Role of RecN in Recombinational DNA Repair and Survival of Helicobacter pylori

2007 ◽  
Vol 76 (1) ◽  
pp. 153-160 ◽  
Author(s):  
Ge Wang ◽  
Robert J. Maier
Keyword(s):  
Helicobacter Pylori ◽  
Parent Strain ◽  
Dna Recombination ◽  
Double Strand Breaks ◽  
Recombinational Repair ◽  
Wild Type ◽  
Dna Double Strand Breaks ◽  
Air Exposure ◽  
Strand Breaks ◽  
H Pylori

ABSTRACT Homologous recombination is one of the key mechanisms responsible for the repair of DNA double-strand breaks. Recombinational repair normally requires a battery of proteins, each with specific DNA recognition, strand transfer, resolution, or other functions. Helicobacter pylori lacks many of the proteins normally involved in the early stage (presynapsis) of recombinational repair, but it has a RecN homologue with an unclear function. A recN mutant strain of H. pylori was shown to be much more sensitive than its parent to mitomycin C, an agent predominantly causing DNA double-strand breaks. The recN strain was unable to survive exposure to either air or acid as well as the parent strain, and air exposure resulted in no viable recN cells recovered after 8 h. In oxidative stress conditions (i.e., air exposure), a recN strain accumulated significantly more damaged (multiply fragmented) DNA than the parent strain. To assess the DNA recombination abilities of strains, their transformation abilities were compared by separately monitoring transformation using H. pylori DNA fragments containing either a site-specific mutation (conferring rifampin resistance) or a large insertion (kanamycin resistance cassette). The transformation frequencies using the two types of DNA donor were 10- and 50-fold lower, respectively, for the recN strain than for the wild type, indicating that RecN plays an important role in facilitating DNA recombination. In two separate mouse colonization experiments, the recN strain colonized most of the stomachs, but the average number of recovered cells was 10-fold less for the mutant than for the parent strain (a statistically significant difference). Complementation of the recN strain by chromosomal insertion of a functional recN gene restored both the recombination frequency and mouse colonization ability to the wild-type levels. Thus, H. pylori RecN, as a component of DNA recombinational repair, plays a significant role in H. pylori survival in vivo.

scholarly journals Mdt1 Facilitates Efficient Repair of Blocked DNA Double-Strand Breaks and Recombinational Maintenance of Telomeres

2007 ◽  
Vol 27 (18) ◽  
pp. 6532-6545 ◽  
Author(s):  
Brietta L. Pike ◽  
Jörg Heierhorst
Keyword(s):  
Dna Recombination ◽  
Double Strand Breaks ◽  
Telomere Maintenance ◽  
Type I ◽  
Dna Double Strand Breaks ◽  
Drug Induced ◽  
Exogenous Dna ◽  
Strand Breaks ◽  
Dramatic Shift ◽  
Recombination Pathway

ABSTRACT DNA recombination plays critical roles in DNA repair and alternative telomere maintenance. Here we show that absence of the SQ/TQ cluster domain-containing protein Mdt1 (Ybl051c) renders Saccharomyces cerevisiae particularly hypersensitive to bleomycin, a drug that causes 3′-phospho-glycolate-blocked DNA double-strand breaks (DSBs). mdt1Δ also hypersensitizes partially recombination-defective cells to camptothecin-induced 3′-phospho-tyrosyl protein-blocked DSBs. Remarkably, whereas mdt1Δ cells are unable to restore broken chromosomes after bleomycin treatment, they efficiently repair “clean” endonuclease-generated DSBs. Epistasis analyses indicate that MDT1 acts in the repair of bleomycin-induced DSBs by regulating the efficiency of the homologous recombination pathway as well as telomere-related functions of the KU complex. Moreover, mdt1Δ leads to severe synthetic growth defects with a deletion of the recombination facilitator and telomere-positioning factor gene CTF18 already in the absence of exogenous DNA damage. Importantly, mdt1Δ causes a dramatic shift from the usually prevalent type II to the less-efficient type I pathway of recombinational telomere maintenance in the absence of telomerase in liquid senescence assays. As telomeres resemble protein-blocked DSBs, the results indicate that Mdt1 acts in a novel blocked-end-specific recombination pathway that is required for the efficiency of both drug-induced DSB repair and telomerase-independent telomere maintenance.

scholarly journals Chlamydia trachomatis Inhibits Homologous Recombination Repair of DNA Breaks by Interfering with PP2A Signaling

mBio ◽  
2018 ◽  
Vol 9 (6) ◽  
Author(s):  
Yang Mi ◽  
Rajendra Kumar Gurumurthy ◽  
Piotr K. Zadora ◽  
Thomas F. Meyer ◽  
Cindrilla Chumduri
Keyword(s):  
Cell Cycle ◽  
Chlamydia Trachomatis ◽  
Homologous Recombination ◽  
Double Strand Breaks ◽  
Host Cells ◽  
Dna Double Strand Breaks ◽  
Content Type ◽  
Strand Breaks ◽  
Recombination Repair ◽  
Infected Cells

ABSTRACT Cervical and ovarian cancers exhibit characteristic mutational signatures that are reminiscent of mutational processes, including defective homologous recombination (HR) repair. How these mutational processes are initiated during carcinogenesis is largely unclear. Chlamydia trachomatis infections are epidemiologically associated with cervical and ovarian cancers. Previously, we showed that C. trachomatis induces DNA double-strand breaks (DSBs) but suppresses Ataxia-telangiectasia mutated (ATM) activation and cell cycle checkpoints. The mechanisms by which ATM regulation is modulated and its consequences for the repair pathway in C. trachomatis-infected cells remain unknown. Here, we found that Chlamydia bacteria interfere with the usual response of PP2A to DSBs. As a result, PP2A activity remains high, as the level of inhibitory phosphorylation at Y307 remains unchanged following C. trachomatis-induced DSBs. Protein-protein interaction analysis revealed that C. trachomatis facilitates persistent interactions of PP2A with ATM, thus suppressing ATM activation. This correlated with a remarkable lack of homologous recombination (HR) repair in C. trachomatis-infected cells. Chemical inhibition of PP2A activity in infected cells released ATM from PP2A, resulting in ATM phosphorylation. Activated ATM was then recruited to DSBs and initiated downstream signaling, including phosphorylation of MRE11 and NBS1 and checkpoint kinase 2 (Chk2)-mediated activation of the G2/M cell cycle checkpoint in C. trachomatis-infected cells. Further, PP2A inhibition led to the restoration of C. trachomatis-suppressed HR DNA repair function. Taking the data together, this study revealed that C. trachomatis modulates PP2A signaling to suppress ATM activation to prevent cell cycle arrest, thus contributing to a deficient high-fidelity HR pathway and a conducive environment for mutagenesis. IMPORTANCE Chlamydia trachomatis induces DNA double-strand breaks in host cells but simultaneously inhibits proper DNA damage response and repair mechanisms. This may render host cells prone to loss of genetic integrity and transformation. Here we show that C. trachomatis prevents activation of the key DNA damage response mediator ATM by preventing the release from PP2A, leading to a complete absence of homologous recombination repair in host cells.

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