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Genetics and Molecular Biology |
9-desaturase genes, ole1 and ole2, from Mortierella alpina complement the yeast ole1 mutation
Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK1
School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK2
Horticulture Research International, Wellesbourne, Warwick CV35 9EF, UK3
Author for correspondence: Donald A. MacKenzie. Tel: +44 1603 255255. Fax: +44 1603 507723. e-mail: donald.mackenzie{at}bbsrc.ac.uk
Genes encoding two distinct fatty acid 
9-desaturases were isolated from strains of the oleaginous fungus Mortierella alpina. Two genomic sequences, 9-1 and 9-2, each containing a single intron, were cloned from strain CBS 528.72 while one cDNA clone, LM9, was isolated from strain CBS 210.32. The 9-1 gene encoded a protein of 445 aa which shared 99% identity with the LM9 gene product. These proteins also showed 40–60% identity to the 9-desaturases (Ole1p) of other fungi and contained the three conserved histidine boxes, C-terminal cytochrome b5 fusion and transmembrane domains characteristic of endoplasmic reticulum membrane-bound 9-desaturases. LM9 and 9-1 are therefore considered to represent the same gene (ole1). The ole1 gene was transcriptionally active in all M. alpina strains tested and its function was confirmed by complementation of the Saccharomyces cerevisiae ole1 mutation. Fatty acid analysis of yeast transformants expressing the CBS 210.32 ole1 gene showed an elevated level of oleic acid (18:1) compared to palmitoleic acid (16:1), the major fatty acid component of wild-type S. cerevisiae. This indicated that the M. alpina 9-desaturase had a substrate preference for stearic acid (18:0) rather than palmitic acid (16:0). Genomic clone 9-2 (ole2) also encoded a protein of 445 aa which had 86% identity to the 9-1 and LM9 proteins and whose ORF also complemented the yeast ole1 mutation. The transcript from this gene could only be detected in one of the six M. alpina strains tested, suggesting that its expression may be strain-specific or induced under certain physiological conditions.
Keywords: Mortierella alpina, 9-desaturase genes, yeast complementation, fatty acid desaturation, oleaginous fungus
Abbreviations: 16:0, palmitic acid; 16:1, palmitoleic acid; 18:0, stearic acid; 18:1, oleic acid; 18:2, linoleic acid; 18:3, 
-linolenic acid; 
-18:3, -linolenic acid; 20:3, dihomo--linolenic acid; 20:4, arachidonic acid (ARA); ER, endoplasmic reticulum; LCPUFA, long-chain polyunsaturated fatty acid; RACE, rapid amplification of cDNA ends; UTR, untranslated region
The GenBank/EMBL accession numbers for the sequences reported in this paper are Y18553 and Y18554 (CBS 528.72 ole1 and ole2 genomic sequences, respectively) and AF0085500 (CBS 210.32 ole1 cDNA).
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