Fig. 8.

Proposed biosynthesis of ustiloxin B. UstA is processed by the endoproteinase Kex2 at the C-terminus in the Golgi apparatus resulting in 16 copies of the precursor peptide. The C-terminus of each precursor peptide is then cleaved by peptidases UstP and UstH to afford a nonapeptide containing a leader and core peptide (underlined). While still attached to the leader peptide, the core YAIG peptide is cyclized. The leader peptide is then cleaved by UstP and UstH affording ustiloxin F. Methylation by UstM is follow by attachment and modification of norvaline by UstF, S, D, and C yielding ustiloxin F. Adapted from Umemura et al.¹⁷⁾.