Figure 1.
Substrate cyclization by terminal cyclization domains and Claisen condensation by the KS domain. A, proposed cyclization model by the KS domain in TAS1. B, classic function of KS domains in PKS that leads to C–C bond formation by Claisen condensation for ketide extension. C, release through cyclization by the TE domain in bacterial NRPS (AntD), cyclization by the CT domain in fungal NRPS (TqaA), and reduction by the R domain in fungal PKS–NRPS hybrid (CpaS), which is followed by spontaneous cyclization. NRPS domains are colored blue and PKS domains are yellow.