Separation-based approach to study dissociation kinetics of noncovalent DNA-multiple protein complexes

Noncovalent binding of DNA with multiple proteins is pivotal to many regulatory cellular processes. Due to the lack of experimental approaches, the kinetics of assembly and disassembly of DNA-multiple proteins complexes have never been studied. Here, we report on a first method capable of measuring disassembly kinetics of such complexes. The method is based on continuous spatial separation of different complexes. The kinetics of multiple complex dissociation processes are also spatially separated, which in turn facilitates finding their rate constants. Our separation-based approach was compared with a conventional no-separation approach by using computer simulation of dissociation kinetics. It proved to be much more accurate than the no-separation approach and to be a powerful tool for testing hypothetical mechanisms of the disassembly of DNA-multiple proteins complexes. An experimental implementation of the separation-based approach was finally demonstrated by using capillary electrophoresis as a separation method. The interaction between an 80 nucleotide long single-stranded DNA and single-stranded DNA binding protein was studied. DNA-protein complexes with one and two proteins were observed, and rate constants of their dissociation were determined. We foresee that a separation approach will be also developed to study the kinetics of the formation of DNA-multiple protein complexes.