Abstract
Chromosome and plasmid segregation is a key cellular function mediated by ParABS system, comprised of ParA, ParB and parS, in prokaryotic cells. ParB binds specifically to parS sites and spreads along parS sites by nearest-neighbor interaction to form a nucleoprotein. The physiological functions of ParB is recruiting structural maintenance of chromosomes (SMC) and chromosome segregation. Recently, ParB is reported possessing bridging activity and can form high-order complexes. However, the high-order complex formation of ParB is not well-proven. In this thesis, we first try to solve the structure of HpSpo0J, chromosome-encoded ParB protein in Helicobacter pylori, to get insight into the function of ParB. Specific and non-specific DNA binding of HpSpo0J were observed by 4parS-290 (290 bp DNA containing 4 parS sites) by electrophoretic mobility shift assay (EMSA). The results of dynamic light scattering (DLS) show HpSpo0J and 4parS-290 form the complex that its radius is ~50 nm. In transmission electron microscopy (TEM) results, 4parS-290 DNA is condensed by HpSpo0J through bridging and spreading interactions and forms thick nucleoprotein filaments, ~35x15 nm and~100x20 nm in basis. HpSpo0J not only can bridge DNA to from an interval loop (~35x15 nm complex), but also can bridge different DNA (~100x20 nm complex).