Polymerization of E83Q and R85Q in presence of ZipA. (A) The polymerization of the FtsZ mutants and wild type was followed by light scattering; the buffer and protein concentrations were the same as described in Figure 4. After a stable base line of the buffer containing 1mM GTP, with or without ZipA, FtsZ was added to initiate the polymerization reaction. The change in light scattering at 350 nm was recorded during the polymerization reaction and the difference between the base line and the maximum value reached after FtsZ addition is shown in the bar graph. (B) Electron microscopy of negatively stained polymers of wild type FtsZ, E83Q and R85Q polymerized as in (A). The samples for FtsZ WT, E83Q and R85Q were taken at 23 min, 53 min and 2h 50 min, respectively (see Additional file 1: Figure S4 for polymerization curves). Electron micrographs were taken at a magnification of 28,500 for wild type FtsZ and E83Q, and of 52,000 for R85Q. Scale bar, 50 nm. (C) Histogram of FtsZ polymers width distribution shows that the mutations E83Q and R85Q decrease the number of protofilaments per polymer. At least 31 polymers were measured for each case using ImageJ.