Fig. 4.

Accumulation of different sterols in erg mutants. (A) Structures of the expected predominant sterols for each mutant strain. In the double mutant erg4Δ erg5Δ, the remaining sterol biosynthetic route ends in the production of ergosta-5,7,24(28)-trienol, whereas in the single mutant erg4Δ, the lack of sterol C-24 reductase activity produces the accumulation of ergosta-5,7,22,24(28)-tetraenol. As Erg4 sterol C-24 reductase activity can use ergosta-5,7,24(28)-trienol as a substrate, the predominant sterol in the erg5Δ strain should be ergosta-5,7-dienol. (B) Semiquantitative analysis of accumulated sterols. Free sterols were further purified and analyzed by mass spectrometry. The normalized peak areas of the protonated sterols in the MS1 are shown. Original spectra are depicted in Figs. S3–S5.