Oscillation helps to get division right.

A conserved feature of proliferating cells is their need to divide at the appropriate time and place using precise positioning mechanisms to ensure that each daughter cell has the same genetic complement as the parent, as well as the correct shape and size. In rod-shaped bacteria, division typically occurs precisely at midcell after the bacterial chromosome has replicated and segregated away from the cell center (1–3) (Fig. 1, Top), thereby generating daughter cells with the same chromosome content and shape as their parent. Early genetic studies in Escherichia coli identified three Min (Minicell) genes whose products are important for defining the normal pattern of cell division. Mutations in these genes lead to inappropriate divisions close to the cell poles, generating chromosome-less minicells. Because Min mutants still undergo cell divisions at midcell in addition to polar divisions (1, 3), precise chromosome positioning, and perhaps other processes, must act additionally to define midcell (3, 4). Subsequent genetic, biochemical, and cell biological studies have revealed features of how the three Min proteins function (3, 5–9). ATP binding to MinD promotes its dimerization and inner membrane binding, whereas its partner protein, dimeric MinE, interacts with MinD to stimulate its ATPase and consequent release from the membrane. The ensuing dynamic pattern of MinD ATPase imparts positional information to the cell (discussed below). A third protein, MinC, which binds and travels as a passenger with MinD, is a division inhibitor but is not required for dynamic patterning. In PNAS, Vecchiarelli et al. (10) extend their analysis of MinCD behavior on supported lipid bilayers in vitro to provide much needed new mechanistic insight into the dynamic patterning mechanism, which helps direct the spatial positioning of division. The work reveals the nonlinear protein interactions that drive the observed Min oscillatory behavior and demonstrates roles of MinD and MinE in patterning additional to those identified in earlier studies. Early live-cell imaging studies showed that the Min proteins oscillate from one cell pole to the other, with a period of <1 min, in reactions requiring MinD andMinE (Fig. 1, Top) (3, 5–7). The oscillations result from the Fig. 1. (Top) Schematic of the oscillatory behavior of MinD (blue, and its passenger, MinC, which exhibits identical oscillatory behavior; not shown) as E. coli cells grow and divide. MinE also oscillates, forming a ring at the leading edge of MinD (for simplicity, not shown). Cells can divide when newly replicated nucleoids have segregated away from the cell center and the divisome has assembled at midcell, where the time-averaged MinC concentration is at a minimum. The bacterial nucleoids are shown in gray. (Bottom) Schematic of the experimental flowcell setup in ref. 10, with the gradient of MinD cartooned. Examples of spirals (solution MinD concentration relatively high; MinD in blue and MinE in red) and bursts (solution MinD concentration low) are shown. For further details, including movies of spiral and burst dynamics, see ref. 10.