Datensatz

Zusammenfassung

The accurate partitioning of Firmicute plasmid pSM19035 at cell division depends on ATP binding and hydrolysis by homodimeric ATPase {delta}2 (ParA) and binding of {omega}2 (ParB) to its cognate parS DNA. The 1.83 Å resolution crystal structure of {delta}2 in a complex with non-hydrolyzable ATP{gamma}S reveals a unique ParA dimer assembly that permits nucleotide exchange without requiring dissociation into monomers. In vitro, {delta}2 had minimal ATPase activity in the absence of {omega}2 and parS DNA. However, stoichiometric amounts of {omega}2 and parS DNA stimulated the {delta}2 ATPase activity and mediated plasmid pairing, whereas at high (4:1) {omega}2 : {delta}2 ratios, stimulation of the ATPase activity was reduced and {delta}2 polymerized onto DNA. Stimulation of the {delta}2 ATPase activity and its polymerization on DNA required ability of {omega}2 to bind parS DNA and its N-terminus. In vivo experiments showed that {delta}2 alone associated with the nucleoid, and in the presence of {omega}2 and parS DNA, {delta}2 oscillated between the nucleoid and the cell poles and formed spiral-like structures. Our studies indicate that the molar {omega}2 : {delta}2 ratio regulates the polymerization properties of ({delta}•ATP•Mg2+)2 on and depolymerization from parS DNA, thereby controlling the temporal and spatial segregation of pSM19035 before cell division.