Figure 1.

The sterol C-5 desaturases ERG-10a and ERG-10b have a redundant function in ergosterol biosynthesis in N. crassa. (A) Structure of ergosterol. Enzymes and their functions mediating double-bond arrangements in ergosterol precursors are depicted (S. cerevisiae/N. crassa). Numbers along ergosterol denote the position of selected carbon atoms, and letters indicate the carbon rings. (B) Late steps in the hypothetical biosynthesis pathway of ergosterol in N. crassa showing the reactions catalyzed by the enzymes presented in (A). ERG-10a and ERG-10b mediate the same reaction, whose block results in the accumulation of a sterol intermediate with an altered ring structure (gray arrow).