FIG. 5.

Hypothetical model of PTT formation based on the modular and domain organization of the PTT assembly system from the PTT gene cluster. Various possibilities for the stage of assembly at which methylation is possible are indicated. C, NRPS condensation domain; A, NRPS adenylation domain; T, NRPS thiolation domain; Te, thioesterase). This is one model of just two: another possibility would place PhsC between PhsA and PhsB. Roles of both thioesterases of type 2 are still speculative. For further explanation see text.