The bacterial nucleoid forms a large, highly organized structure. Thus, in addition to storing the genetic code, the nucleoid harbors positional information that can be leveraged by DNA-binding proteins to spatially constrain cellular activities. During B. subtilis sporulation, the nucleoid undergoes reorganization, and the cell division protein FtsZ assembles polarly to direct septation over one chromosome. The TetR family protein RefZ binds DNA motifs (RBMs) localized near the poles at the time of division and is required for both timely FtsZ assembly and precise capture of DNA in the future spore compartment. Our data suggest that RefZ exploits nucleoid organization by associating with polarly localized RBMs to modulate the positioning of FtsZ relative to the chromosome during sporulation.
Positions of residues implicated in RefZ’s regulation of cell division.
(A) Surface/cartoon representation of the RefZ homodimer highlighting residues with substitutions conferring loss of function (red; sticks). The subunits are colored white and cyan. (B) Ribbon model of the RefZ region showing residues conferring loss of function as sticks.
(C and E) Surface/cartoon representations of the SlmA homodimer (unbound) (PDB ID 3NXC) (28) (C) and the SlmA homodimer bound to DNA and the CTD tail of FtsZ (PDB ID 5HBU) (26) (E), highlighting residues with substitutions conferring loss of function (red; sticks). The subunits are colored white and green.
(D and F) Ribbon models corresponding to the SlmA homodimer (PDB ID 3NXC) (28) (D) and SlmA homodimer bound to DNA and the CTD tail of FtsZ (PDB ID 5HBU) (26) (F), showing residues conferring loss of function as sticks.