The nysF gene encoding a putative 4'-phosphopantetheinyl transferase (PPTase) is located at the 5' border of the nystatin biosynthesis gene cluster in Streptomyces noursei. PPTases carry out post-translational modification of the acyl carrier protein domains on the polyketide synthases (PKS) required for their full functionality, and hence NysF was assumed to be involved in similar modification of the nystatin PKS. At the same time, DNA sequence analysis of the genomic region adjacent to the nysF gene revealed a gene cluster for a putative lantibiotic biosynthesis. This finding created some uncertainty regarding which gene cluster nysF functionally belongs to. To resolve this ambiguity, nysF was inactivated by both insertion of a kanamycin (Km) resistance marker into its coding region, and by in-frame deletion. Surprisingly, the nystatin production in both the nysF::Km(R) and DeltanysF mutants increased by ca. 60% compared to the wild-type, suggesting a negative role of nysF in the nystatin biosynthesis. The expression of xylE reporter gene under control of different promoters from the nystatin gene cluster in the DeltanysF mutant was studied. The data obtained clearly show enhanced expression of xylE from the promoters of several structural and regulatory genes in the DeltanysF mutant, implying that NysF negatively regulates the nystatin biosynthesis.

A regulatory gene locus from Streptomyces noursei ATCC14455, the producer of the antifungal antibiotic nystatin, was cloned in Streptomyces lividans based on its ability to activate actinorhodin (Act) production in this host. Deletion and DNA sequencing analyses showed that a small gene, designated ssmA, located downstream of an afsR homologue (a known pleiotropic regulator) was responsible for the Act overproduction in S. lividans. Database searches for the ssmA gene product revealed its limited similarity to the AfsR2 regulatory protein from S. lividans and CREA catabolite repressor from Aspergillus nidulans. To study the effect of ssmA on nystatin production, this gene was either deleted from S. noursei genome, or placed under control of PermE* promoter and introduced in S. noursei. The properties of the corresponding strains indicate that ssmA is involved in regulation of growth and antibiotic production only in the media with certain carbon sources.