The erg-3 (sterol delta14,15-reductase) gene of Neurospora crassa: generation of null mutants by repeat-induced point mutation and complementation by proteins chimeric for human lamin B receptor sequences.

Null mutations were generated in the erg-3 gene of Neurospora crassa by repeat-induced point mutation (RIP). The mutants were viable, lacked ergosterol, were resistant to the steroidal glycoside alpha-tomatine and were sensitive to the phytoalexins pisatin and biochanin A. RIP was frequently associated with silencing of the hph gene located adjacent to the duplicated erg-3 sequence. The silencing of hph was reversible in the two cases examined and appeared to be due to the spread of cytosine methylation associated with RIP. The erg-3 mutant could be complemented by transformation with recombinant genes that encode proteins chimeric for amino acid sequences from the transmembrane (TM) domain of human lamin B receptor (LBR). This indicates that the LBR TM domain possesses delta14,15-reductase activity.