HUMAN LAMIN-B RECEPTOR EXHIBITS STEROL C-14-REDUCTASE ACTIVITY IN SACCHAROMYCES-CEREVISIAE

Lamin B receptor (LBR), a nuclear protein of avian and mammalian cells , contains an hydrophobic domain that shares extensive structural simi larities with the members of the sterol reductase family. To test if t he sterol-reductase-like domain of LBR could be enzymatically competen t, several sterol reductase-defective strains of Saccharomyces cerevis iae were transformed with a human-LBR expressing vector. LBR productio n did not change the ergosterol biosynthesis defect in an erg4 mutant impaired in sterol C24(28) reductase. In contrast, the sterol C14 redu ction step and ergosterol prototrophy were restored in LBR-producing e rg24 transformants which lack endogenous sterol C14 reductase. To test the effects of C14 reductase inhibitors on LBR activity, we construct ed EMY54, an ergosterol-requiring strain that is devoid of both sterol C8-C7 isomerase and sterol C14 reductase activities. EMY54 cells reco vered the capability of synthesizing ergost-8-en-3 beta-ol upon transf ormation with a vector that expressed either yeast sterol C14 reductas e or hLBR. In addition, growth in sterol-free medium was restored in t hese transformants. Sterol biosynthesis and proliferation of LBR-produ cing cells were found to be highly susceptible to fenpropimorph and tr idemorph, but only moderately susceptible to SR 31747. Our results str ongly suggest that hLBR is a sterol C14 reductase. (C) 1998 Elsevier S cience B.V.