In order to characterize C. difficile Spo0A, the full length protein and its DNA binding domain (DBD) were expressed as a Cterminally 66His-tagged protein in the heterologous host Escherichia coli (Fig. 1A) and purified to near homogeneity using metal affinity chromatography ( Fig. 1A ; lanes P). Full length protein was used to raise antibodies to detect Spo0A in total lysates of C. difficile strains, and the purified DNA binding domain was used in subsequent in vitro binding assays (see below).