Negatively stained preparations of monolayer crystallites obtained by using the fraction of the water-soluble (monomeric and/or oligomeric) (A to C) or the GlcNAc-extracted and dialyzed (D) S-layer protein from B. stearothermophilus PV72/p2 for recrystallization on poly-l-lysine-coated EM grids. (A to C) To keep the S-layer protein in the water-soluble state, different amounts of SCWP were added to the GHCl-extracted S-layer protein, and the solutions were dialyzed against 10 mM CaCl2. The size of the individual crystallites correlated with the amount of added SCWP: 60 (A), 150 (B), and 250 (C) μg of SCWP/mg of S-layer protein. (D) Monolayer crystallites were also formed by the GlcNAc-extracted dialyzed S-layer protein. In both cases, the S-layer subunits had bound with their charge-neutral outer face. Arrows indicate base vectors. Bars, 200 nm.