FIGURE 1.

The proposed biosynthetic pathway of GAL. A, a schematic representation of the GAL macrolactone backbone assembly line and the proposed biosynthetic pathway. B, the proposed role of GalA-E in GAL biosynthesis; the intermediacy of GAL-C in GAL-B biogenesis is described. For simplicity, the stereochemistry in each chiral center is not shown in the structure but is instead indicated by R or S. GalB harbors a truncated KS domain. GalC is homologous to known KSs but lacks the catalytic Cys residue. Both are indicated as ψKS to denote that they are non-canonical KSs.