Staggered Extension Process In Vitro DNA Recombination

Author(s):  
Huimin Zhao
2001 ◽  
Vol 12 (5) ◽  
pp. 1199-1213 ◽  
Author(s):  
Gregory G. Oakley ◽  
Lisa I. Loberg ◽  
Jiaqin Yao ◽  
Mary A. Risinger ◽  
Remy L. Yunker ◽  
...  

Exposure to DNA-damaging agents triggers signal transduction pathways that are thought to play a role in maintenance of genomic stability. A key protein in the cellular processes of nucleotide excision repair, DNA recombination, and DNA double-strand break repair is the single-stranded DNA binding protein, RPA. We showed previously that the p34 subunit of RPA becomes hyperphosphorylated as a delayed response (4–8 h) to UV radiation (10–30 J/m2). Here we show that UV-induced RPA-p34 hyperphosphorylation depends on expression of ATM, the product of the gene mutated in the human genetic disorder ataxia telangiectasia (A-T). UV-induced RPA-p34 hyperphosphorylation was not observed in A-T cells, but this response was restored by ATM expression. Furthermore, purified ATM kinase phosphorylates the p34 subunit of RPA complex in vitro at many of the same sites that are phosphorylated in vivo after UV radiation. Induction of this DNA damage response was also dependent on DNA replication; inhibition of DNA replication by aphidicolin prevented induction of RPA-p34 hyperphosphorylation by UV radiation. We postulate that this pathway is triggered by the accumulation of aberrant DNA replication intermediates, resulting from DNA replication fork blockage by UV photoproducts. Further, we suggest that RPA-p34 is hyperphosphorylated as a participant in the recombinational postreplication repair of these replication products. Successful resolution of these replication intermediates reduces the accumulation of chromosomal aberrations that would otherwise occur as a consequence of UV radiation.


2003 ◽  
pp. 99-104
Author(s):  
Olga Esteban ◽  
Ryan D. Woodyer ◽  
Huimin Zhao

2006 ◽  
Vol 1 (4) ◽  
pp. 1865-1871 ◽  
Author(s):  
Huimin Zhao ◽  
Wenjuan Zha

2007 ◽  
Vol 189 (12) ◽  
pp. 4502-4509 ◽  
Author(s):  
Syam P. Anand ◽  
Haocheng Zheng ◽  
Piero R. Bianco ◽  
Sanford H. Leuba ◽  
Saleem A. Khan

ABSTRACT PcrA is a conserved DNA helicase present in all gram-positive bacteria. Bacteria lacking PcrA show high levels of recombination. Lethality induced by PcrA depletion can be overcome by suppressor mutations in the recombination genes recFOR. RecFOR proteins load RecA onto single-stranded DNA during recombination. Here we test whether an essential function of PcrA is to interfere with RecA-mediated DNA recombination in vitro. We demonstrate that PcrA can inhibit the RecA-mediated DNA strand exchange reaction in vitro. Furthermore, PcrA displaced RecA from RecA nucleoprotein filaments. Interestingly, helicase mutants of PcrA also displaced RecA from DNA and inhibited RecA-mediated DNA strand exchange. Employing a novel single-pair fluorescence resonance energy transfer-based assay, we demonstrate a lengthening of double-stranded DNA upon polymerization of RecA and show that PcrA and its helicase mutants can reverse this process. Our results show that the displacement of RecA from DNA by PcrA is not dependent on its translocase activity. Further, our results show that the helicase activity of PcrA, although not essential, might play a facilitatory role in the RecA displacement reaction.


Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 3898-3898
Author(s):  
Andrea Cerutti ◽  
Bing He ◽  
April Chiu ◽  
Meimei Shan ◽  
Paul Santini ◽  
...  

Abstract Introduction. Class switching from IgM to IgG and IgA is central to immunity against microbes and usually occurs in draining lymph nodes and requires activation of B cells by CD4+ T cells expressing CD40 ligand. Growing evidence indicates that B cells can mount frontline IgG and IgA responses at mucosal sites of entry through an alternative CD40-independent pathway involving B cell-activating factor of the TNF family (BAFF, also known as BLyS) and a proliferation-inducing ligand (APRIL). These innate factors are usually produced by dendritic cells and stimulate B cells through at least three distinct receptors. Together with dendritic cells, epithelial cells have a key position at the host-environment interface. Therefore, we asked whether epithelial cells play a role in frontline antibody production. Methods. Tonsillar tissue sections from healthy donors were analyzed for expression of activation-induced cytidine deaminase (AID) by immunohistochemistry and in situ hybridization. A simplified in vitro model reproducing the geometry of mucosal surfaces was used to evaluate the role of epithelial cells in class switching. Briefly, primary epithelial cells and B cells were cultured in the upper and lower chambers, respectively, of a trans-well system. Monocyte-derived dendritic cells were positioned on a filter separating the two chambers. Various microbial product analogues were used to mimic infection. RNA interference was performed to knockdown BAFF in epithelial cells. AID expression, CSR, antibody production and signaling were evaluated in B cells as reported (Litinsky et al., Nat. Immunol.2002, 3:822–829; Qiao et al., Nat. Immunol.2006, 7:302–310). Results. We found that the upper respiratory mucosa of healthy subjects comprised intraepithelial pockets filled with B cells expressing AID, a DNA-editing enzyme associated with ongoing class switch DNA recombination (CSR). Epithelial cells released innate class switch-inducing factors, including BAFF, after sensing microbial products through TLRs, thereby inducing AID expression, CSR, and ultimately IgG and IgA production in neighboring B cells. Epithelial cell-induced antibodies comprised polyreactive IgG and IgA capable of recognizing multiple microbial determinants. Intraepithelial class switching was enhanced by thymic stromal lymphopoietin (TSLP), an epithelial IL-7-like cytokine that augments the innate B cell-licensing functions of dendritic cells, and restrained by secretory leukocyte protease inhibitor (SLPI), an epithelial alarm antiprotease that suppresses AID expression in activated B cells. Conclusions. The present findings indicate that epithelial cells function as non-immune sentinels capable to autonomously orchestrate compartmentalized IgG and IgA responses at the interface between host and environment. This implies that mucosal vaccines should activate both epithelial and immune cells to elicit optimal antibody production.


2003 ◽  
Vol 51 (4) ◽  
pp. 1143-1154 ◽  
Author(s):  
Stacy K. Merickel ◽  
Reid C. Johnson

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