microbiology, Vol 145, 1443-1451, Copyright © 1999 by Society for General Microbiology

ARTICLES

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

SA Prakash, KA Saswati and DP Kasbekar
Centre for Cellular and Molecular Biology, Hyderabad 500 007, India

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.

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