The erg-3 (sterol Delta(14,15)-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 rep eat-induced point mutation (RIP). The mutants were viable, lacked ergostero l, were resistant to the steroidal glycoside alpha-tomatine and were sensit ive to the phytoalexins pisatin and biochanin A. RIP was frequently associa ted 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 an d appeared to be due to the spread of cytosine methylation associated with RIP. The erg-3 mutant could be complemented by transformation with recombin ant genes that encode proteins chimeric for amino acid sequences from the t ransmembrane (TM) domain of human lamin B receptor (LBR). This indicates th at the LBR TM domain possesses Delta(14,15)-reductase activity.