Fig. 4. Comparison of filament-forming proteins of the actin family of proteins. Eukaryotic actin is shown here in the ADP form (PDB entry 1J6Z). MreB is involved in the maintenance of cell shape in non-spherical bacteria (here shown in complex with AMPPNP; PDB entry 1JCG). ParM forms actin-like filaments in E.coli that are required for segregation of plasmid R1. It is shown here in the ADP form. Colour codes are the same as for Figure 3 (with subdomain IA in blue, IB in yellow, IIA in red and IIB in green). Subdomains IA, IB, IIA and IIB correspond to subdomains 1, 2, 3 and 4 in actin. ParM can be superimposed on 261 C_α atoms of actin (PDB entry 1yag-A) with an r.m.s.d. of 3.3 Å and a Z-score of 20.4. Similarly, it can be superimposed on MreB (PDB entry 1JCF) with an r.m.s.d. of 3.7 Å, for 255 C_α atoms, and a Z-score of 20.3 (Holm and Sander, 1993). As comparison, 310 C_α atoms of MreB superimpose on actin with an r.m.s.d. of 3.7 Å and a Z-score of 29.2 (van den Ent et al., 2001a).