Detection of FK228 positive ion signals by LC-MS. Samples were obtained from an authentic FK228 standard (A), wild-type C. violaceum (B), Cv56a/b/c mutants with the pP3-A6-associated gene inactivated (C), Cv57a/b/c mutants with the pP4-B4-associated depD gene (3′ part) inactivated (D), and Cv58a/b/c mutants with the pP4-G7-associated depD gene inactivated (E). For each mutation three mutants (a, b, and c) yielded identical results; therefore, only one data profile for each mutation is presented.