Functional and physical interaction between WRN helicase and human replication protein A.

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Werner syndrome (WS) is a premature aging disorder linked to mutations in the WRN gene.
• The WRN protein functions as a DNA helicase, previously shown to unwind short DNA duplexes.
• Stimulation by single-stranded DNA-binding proteins was known for short DNA unwinding.

Purpose of the Study:

• To characterize the unwinding properties of purified WRN helicase on various DNA substrates.
• To investigate the specific protein interactions that stimulate WRN helicase activity on longer DNA duplexes.
• To determine if WRN physically interacts with human replication protein A (hRPA).

Main Methods:

• Purification of WRN protein.
• Assays of WRN helicase activity on long DNA duplex substrates (up to 849 base pairs).
• Co-immunoprecipitation assays to detect physical interactions between WRN and hRPA.

Main Results:

• WRN helicase can unwind long DNA duplexes (up to 849 bp) in a reaction dependent on hRPA.
• Bacterial (E. coli SSB) and phage (T4 gp32) single-stranded DNA-binding proteins did not stimulate WRN helicase on long DNA.
• A direct physical interaction between WRN and hRPA was demonstrated via co-immunoprecipitation.

Conclusions:

• WRN helicase activity on long DNA substrates is specifically stimulated by hRPA, not other SSB proteins.
• WRN and hRPA physically interact, suggesting a functional partnership in vivo.
• This interaction implies a role for WRN and hRPA together in DNA metabolism pathways like replication, recombination, or repair.