Related Experiment Video
Updated: Jun 19, 2026
06:24
Real-time Observation of the DNA Strand Exchange Reaction Mediated by Rad51
Published on: February 13, 2019
SSB protein diffusion on single-stranded DNA stimulates RecA filament formation
Rahul Roy1, Alexander G Kozlov, Timothy M Lohman
1Center for Biophysics and Computational Biology, University of Illinois, Urbana-Champaign, Illinois 61801, USA.
Nature
|October 13, 2009
Summary
Single-stranded DNA-binding (SSB) proteins protect DNA but must move for repair. We found tetrameric SSB can migrate along DNA, aiding protein access and DNA repair processes.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Single-stranded DNA (ssDNA) is transiently generated during DNA metabolism.
- ssDNA is stabilized by ssDNA-binding (SSB) proteins to protect it from degradation.
- Escherichia coli SSB is a homotetrameric protein that binds ssDNA by wrapping it.
Purpose of the Study:
- To investigate the dynamics of tetrameric SSB on ssDNA.
- To understand how SSB facilitates access for other DNA-processing proteins.
- To explore the role of SSB dynamics in DNA recombination and repair.
Main Methods:
- Single-molecule two- and three-colour fluorescence resonance energy transfer (FRET).
- Observing the spontaneous migration of tetrameric SSB along ssDNA.
Main Results:
- Tetrameric SSB exhibits spontaneous diffusional migration along ssDNA.
- SSB diffusion facilitates local displacement by elongating RecA filaments.
- SSB migration transiently melts DNA hairpins, promoting RecA filament elongation on structured DNA.
Conclusions:
- SSB proteins can move along ssDNA while remaining bound, challenging previous models.
- Diffusional migration provides a mechanism for SSB redistribution during DNA metabolism.
- This dynamic behavior is crucial for efficient DNA recombination and repair.
Related Concept Videos
01:03Single-Strand DNA Binding Proteins
For successful DNA replication, the unwinding of double-stranded DNA must be accompanied by stabilization and protection of the separated single strands of the DNA. This crucial task is performed by single-strand DNA-binding (SSB) proteins. They bind to the DNA in a sequence-independent manner, which means that the nitrogenous bases of the DNA need not be present in a specific order for binding of SSB proteins to it. The binding of SSB proteins straightens single-stranded DNA (ssDNA) and makes...
01:02The DNA Replication Fork
An organism’s genome needs to be duplicated in an efficient and error-free manner for its growth and survival. The replication fork is a Y-shaped active region where two strands of DNA are separated and replicated continuously. The coupling of DNA unzipping and complementary strand synthesis is a characteristic feature of a replication fork. Organisms with small circular DNA, such as E. coli, often have a single origin of replication; therefore, they have only two replication forks, one in...
00:55DNA Helicases
DNA unwinding helicase enzymes are a type of motor protein. Motor proteins can translocate along filaments or polymers using energy generated from ATP hydrolysis. Helicases are involved in all the important cellular processes where DNA unwinding is required, such as DNA replication, repair, recombination, and transcription. They are present in all living organisms, but vary in their structure, function, and mechanism of action. For example, in prokaryotes, DnaB helicase binds and translocates...
03:01The Replisome
DNA replication is carried out by a large complex of proteins that act in a coordinated matter to achieve high-fidelity DNA replication. Together this complex is known as the DNA replication machinery or the replisome.
The synthesis of the leading and lagging strands is a highly coordinated process. To explain this, the “Trombone model” was proposed by Bruce Alberts in 1980. The DNA loop formation starts when a primer is synthesized on the parent lagging strand. The loop grows with the...
The synthesis of the leading and lagging strands is a highly coordinated process. To explain this, the “Trombone model” was proposed by Bruce Alberts in 1980. The DNA loop formation starts when a primer is synthesized on the parent lagging strand. The loop grows with the...
02:37Restarting Stalled Replication Forks
DNA replication is initiated at sites containing predefined DNA sequences known as origins of replication. DNA is unwound at these sites by the minichromosome maintenance (MCM) helicase and other factors such as Cdc45 and the associated GINS complex.The unwound single strands are protected by replication protein A (RPA) until DNA polymerase starts synthesizing DNA at the 5’ end of the strand in the same direction as the replication fork. To prevent the replication fork from falling apart, a...
02:31Homologous Recombination
The basic reaction of homologous recombination (HR) involves two chromatids that contain DNA sequences sharing a significant stretch of identity. One of these sequences uses a strand from another as a template to synthesize DNA in an enzyme-catalyzed reaction. The final product is a novel amalgamation of the two substrates. To ensure an accurate recombination of sequences, HR is restricted to the S and G2 phases of the cell cycle. At these stages, the DNA has been replicated already and the...