PAXX and its paralogs synergistically direct DNA polymerase λ activity in DNA repair

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• PAXX is a recently identified component of the nonhomologous end joining (NHEJ) DNA repair pathway.
• The precise molecular mechanisms governing PAXX's function in DNA repair are not fully understood.

Purpose of the Study:

• To elucidate the molecular mechanisms of PAXX in DNA repair.
• To characterize the interactomes of PAXX and its paralogs, XLF and XRCC4.
• To identify novel downstream effectors and functions of PAXX within the NHEJ pathway.

Main Methods:

• Proteomic analysis to characterize the interactomes of PAXX, XLF, and XRCC4.
• In vitro assays to assess the interaction and stimulation of DNA polymerase lambda (Pol λ) activity.
• Laser-induced DNA damage assays to evaluate the recruitment of Pol λ in vivo.
• Functional assays to investigate the role of PAXX and XLF in DNA end joining.

Main Results:

• PAXX, XLF, and XRCC4 interact with DNA polymerase lambda (Pol λ).
• These proteins stimulate Pol λ activity and are crucial for its recruitment to DNA damage sites.
• Direct interaction between Pol λ's SP/8 kDa domain and the N-terminal head domains of XRCC4 paralogs is necessary for stimulating polymerase activity.
• PAXX and XLF collaborate with Pol λ to promote the joining of incompatible DNA ends and exhibit redundancy in supporting Pol λ function.
• Pol λ is identified as a novel downstream effector of PAXX.

Conclusions:

• PAXX functions in DNA repair through its interaction with and regulation of DNA polymerase lambda (Pol λ).
• XRCC4 paralogs act synergistically to modulate polymerase activity within the NHEJ pathway.
• PAXX and XLF play collaborative and partially redundant roles with Pol λ in DNA repair processes.