McdA and McdB together mediate carboxysome (Cb) spacing, size, ultrastucture and probably inheritance in the cell, together they prevent Cb aggregation. McdA is an ATPase that forms dynamic gradients on the nucleoid in response to adapter protein McdB, which associates with carboxysomes. The interplay between McdA gradients on the nucleoid and McdB-bound carboxysomes result in the equal spacing of Cbs along the cell length. Binds DNA saturably and strongly in the presence of Mg(2+)ATP; without ATP, DNA-binding is very poor (tested with a mutant that should not be able to hydrolyze ATP, Asp-38-Ala). Decreasing the NaCl concentration increases DNA binding