Analytical ultracentrifugation of MBP-rep. Equilibrium centrifugation data for 1.45, 1.1,and 0.55 μM RamC (◊) were fitted to curves predicted for a monomer, a dimer, a trimer, a tetramer,and a pentamer of a 55-kDa protein. The curves at the top show the residuals representing the accuracy of the dimeric protein model when they were compared to the actual data. AU, absorbance units.