Production of venezuelins in Actinobacteria. (A) Representative gene clusters of GCF147. (B) A logo depicting the GCF147 precursor peptide sequences. (C) MALDI-TOF MS analysis of venezuelin produced by Streptomyces katrae ISP5550. MALDI-TOF MS analysis of venezuelins produced by Streptomyces lavendulae subsp. lavendulae NRRL B-2508 and Streptomyces sp. NRRL B-2375 are shown in Fig. S8 in the supplemental material. (D) ESI-MS-MS analysis of venezuelin produced by S. katrae ISP5550. The lack of fragmentation is consistent with a globular, overlapping ring topology. (E) Chiral GC-MS analysis of hydrolyzed and derivatized venezuelin residues, which revealed the presence of dl-lanthionine and dl-methyllanthionine. Trace i, sample showing the presence of dl-lanthionine; trace ii, sample spiked with dl-lanthionine standard; trace iii, sample showing the presence of dl-methyllanthionine; trace iv, sample spiked with dl-methyllanthionine standard.