(A) Organization of the pcfA, pcfB, pcfI, pcfC, and pcfD genes involved in propionicin F biosynthesis and immunity (GenBank accession no. AY587566). The black bar inside pcfA indicates the part encoding the propionicin F peptide. For further description, see text. (B) The nucleotide sequence and translation of the pcfI immunity gene (GenBank protein accession no. ABU97165.1). Bold characters indicate predicted transmembrane helical segments of the immunity protein analyzed by use of the Toppred algorithm (33).