Cooperativity and intermediate structures of single-stranded DNA binding-assisted RecA-single-stranded DNA complex...

Area of Science:

• Molecular Biology
• Biophysics

Background:

• RecA protein is crucial for DNA repair and recombination.
• Single-stranded DNA binding (SSB) protein modulates DNA interactions.
• Understanding RecA-ssDNA complex formation is key to DNA replication and repair mechanisms.

Purpose of the Study:

• To systematically investigate the early stages of RecA protein and single-stranded DNA complex formation.
• To identify and characterize intermediate structures formed during RecA-ssDNA binding.
• To elucidate the role of single-stranded DNA binding (SSB) protein in modulating RecA-ssDNA interactions.

Main Methods:

• Atomic Force Microscopy (AFM) was employed to visualize complex formation.
• Incubation time and the molecular ratio of RecA to SSB protein were varied.
• Structural intermediates were analyzed at different stages of complex assembly.

Main Results:

• Novel intermediate structures (circular, tangled, protruded, sharply turned) were identified.
• These structures suggest competitive binding between RecA and SSB proteins for DNA.
• Long incubation led to fully formed RecA-ssDNA or SSB-ssDNA complexes.

Conclusions:

• RecA and SSB proteins exhibit competitive binding dynamics with single-stranded DNA.
• SSB protein assists in the strong, cooperative binding of RecA to ssDNA.
• The study provides insights into the mechanism of RecA filament formation on ssDNA.