Fig. 1. Outline of the DIF-1 biosynthetic pathway. The C₁₂ skeleton of DIF-1 is proposed to be assembled by a polyketide synthase and then modified, first by chlorination and then by methylation, to give DIF-1 (Kay, 1998). The methylation step is carried out by the methyltransferase encoded by the dmtA gene (Thompson and Kay, 2000).