Chun J., 2013
Terminology
HR - Homologous recombination
IR - Ionizing radiation
gene conversion - "one DNA sequence replaces a homologous sequence such that the sequences become identical after the conversion event" https://en.wikipedia.org/wiki/Gene_conversion
Resolvase = recombinase = nuclease that involve in DNA recombination
Supress sgs1 hydroxyurea (HU) sensitivity = SHU complex.
Summary
BRAC2 is the main mediator to promote Rad51 filament formation. In the absense of BRCA2, Rad52 drives a secondary pathway for Rad51-dependent HR. Depletion of Rad52 and BRCA2 further reduced HR. Since depletion of any Rad51 paralog did not further reduce the HR in BRCA2-depleted cells, Rad51 paralogs are epistatic with BRCA2.
=> Depletion of BRCA2 causes more significant effects in HR than the depletion of any Rad51 paralog, most likely because BRCA2 holes a direct role in loading Rad51 onto the DSB and Rad51 paralogs are more likely to stabilizing and protecting the Rad51 nucleoprotein filament from antirecombinase.
However, Rad51 paralogs may hold more significant effects in repairing replication-stalling lesions since they have more hypersensitivity to replication-stalling agents (DNA cross linking agents or topoisomerase inhibitors) than IR.
Rad51 carries out the recombinase activities was well studied, and Rad51 paralogs are known to facilitate Rad51 in HR under the IR condition. However, the molecular mechanisms of Rad51 paralogs in this process (Rad51B, Rad51C, Rad51D, XRCC2, XRCC3) still needs further investigation. So, Rad51 paralogs can be divided into 2 complexes, including BCDX2 (consisting of Rad51B, Rad51C, Rad51D, and XRCC2) and CX3 (consisting of Rad51C and XRCC3)
Rad51 paralogs also relate gene conversion tract length and Holiday junction recombinase activity. In mice, diruption of any Rad51 paralog can cause lethality in early embryonic stages and unrepaired DNA accumulation.
The data in this paper suggested that BCDX2 and CX3 affect the HR pathway at different stages, in which BCDX2 acts downstream of BRCA2 recruitment but upstream of Rad51 recruitment to the DSB and stabilizes the damage sites, while CX3 acts downstream of Rad51 filament formation.
Disruption in Rad51C significantly affects the CX3 complex but not BCDX2 complex. Depletion of any Rad51 paralog significantly reduces HR activity demonstrated by measurement of I-SceI-induced homology-mediated repair.
Both Rad51 complexes are necessary for downstream activity of BRCA1 or BRCA2 but before the Rad51 nucleprotein formation. The depletion of CX3 did not affect the Rad51filament formation. However, the depletion of both BCDX2 and CX3 led to a decrease in Rad51 filament formation. Therefore, BCDX2 acts upstream and CX3 acts downstream of the Rad51 recruitment.
Since depletion of any Rad51 paralog with Rad52 further decreased HR frequency measured by amount of I-SceI protein, demonstrating that Rad51 complexes a synthetically lethal relationship with Rad52.
In yeast, Rad51 paralogs (Rad55-Rad57 complex) were known to facilitate Rad51 nucleprotein formation. Yeast Rad55 ~ human XRCC2, yeast Rad57 ~ human Rad51D. The Shu complex prevents the disassembly of Rad51 by Srs2 from DNA. The Shu complex consists of 4 subunits, including Csm2, Psy3, Shu1, and Shu2.
Yeast Shu1 ~ Human XRCC2
Yeast Psy3 ~ Human Rad51D
Yeast Shu2 ~ Human SWS1, which interacts with Rad51 and Rad51 paralogs through hSWS1-associate protein.
Since XRCC3 depletion significantly reduced HR activity but did not alter Rad51 filament formation, therefore, it was hypothesized that CX3 complex is not responsible for Rad51 recruitment to DSB. Depletion of Rad51C can significantly remove CX3 complex, causing more significant damage in the CX3 complex than in the BCDX2.
Need Clarification
- DHJ Holiday junction
- HR
- NHEJ
- SDSA
- Plating efficiency
No comments:
Post a Comment