Figure 1.

Regulation of secondary metabolite gene expression is controlled by cluster situated regulators (CSRs), which can be controlled by binding of pathway products, and global regulatory systems, which are influenced by external environmental factors, such as nutrient availability. Global regulators coordinate primary and secondary metabolism with growth and development. Global regulators can control the expression levels of CSRs, indirectly affecting BGC expression, or bind to elements within BGCs and directly control expression. Some CSRs are also influenced by (and/or can influence) primary metabolism, growth and development. Additionally, some CSRs can cross-regulate the expression of other BGCs in the genome, thereby controlling the levels of multiple secondary metabolites.