Figure 4.

Attachment to a substrate allows a racE null cell to divide. A racE null cell suspended in medium containing less that 0.03% agarose slowly settled onto the substrate. Notice how other attached cells come into the plane of focus. The racE null cell attempts to divide in suspension by forming a cleavage furrow (white arrowhead), but it fails and its furrow begins to regress (black arrowheads). The cell attaches to the coverslip and becomes “phase-dark.” Remarkably, the cell quickly forms a new cleavage furrow (white arrow), which constricts to completion. Each frame = 12 s.