Single-molecule observation of ATP-independent SSB displacement by RecO in Deinococcus radiodurans
Jihee Hwang,
Jae-Yeol Kim,
Cheolhee Kim,
Soojin Park,
Sungmin Joo,
Seong Keun Kim,
Nam Ki Lee
Affiliations
Jihee Hwang
Department of Chemistry, Seoul National University, Seoul, Republic of Korea
Jae-Yeol Kim
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health (NIH), Bethesda, United States
Cheolhee Kim
Daegu National Science Museum, Daegu, Republic of Korea
Soojin Park
Department of Chemistry, Seoul National University, Seoul, Republic of Korea
Sungmin Joo
Department of Physics, Pohang University of Science and Technology, Pohang, Republic of Korea
Seong Keun Kim
Department of Chemistry, Seoul National University, Seoul, Republic of Korea
Deinococcus radiodurans (DR) survives in the presence of hundreds of double-stranded DNA (dsDNA) breaks by efficiently repairing such breaks. RecO, a protein that is essential for the extreme radioresistance of DR, is one of the major recombination mediator proteins in the RecA-loading process in the RecFOR pathway. However, how RecO participates in the RecA-loading process is still unclear. In this work, we investigated the function of drRecO using single-molecule techniques. We found that drRecO competes with the ssDNA-binding protein (drSSB) for binding to the freely exposed ssDNA, and efficiently displaces drSSB from ssDNA without consuming ATP. drRecO replaces drSSB and dissociates it completely from ssDNA even though drSSB binds to ssDNA approximately 300 times more strongly than drRecO does. We suggest that drRecO facilitates the loading of RecA onto drSSB-coated ssDNA by utilizing a small drSSB-free space on ssDNA that is generated by the fast diffusion of drSSB on ssDNA.
