Design of recombinant CS6 subunit monomers and fusion proteins. (A) Initial CS6 subunit fusions with homologous donor strand complementation, the donor strand fused to the C terminus derived from the C-terminal protein. The CssA protein is denoted in solid blue shading, the CssB protein is in solid red shading, the donor strand of CssA is in blue diagonal shading, the donor strand of CssB is in red diagonal shading, the DNKQ linker sequence is in black shading, and the hexahistidine tag is in green shading. (B and C) SDS-PAGE (B) and anti-CS6 Western blot (C) analyses of homologous donor strand-complemented CssA and CssB monomer and multimeric fusions. Lane 1, dscACssA; lane 2, dscBCssB; lane 3, dscACssAA; lane 4, dscBCssBB; lane 5, dscBCssAB; lane 6, dscACssBA; lane 7, dscACssABA; lane 8, dscBCssABB; lane 9, dscACssBBA; lane 10, dscBCssBAB; lane 11, dscACssBAA. Anti-CS6 sera were used at a concentration of 1:106, with the exception of dscACssA, which was blotted with an antibody concentration of 1:105. Abbreviations: ntd, deletion of the N-terminal donor strand; dsc, donor strand complementation of the C-terminal protein with the donor strand from either CssA (dscA) or CssB (dscB); MW, molecular weight.