The genes encoding the enzymes of the entire ergosterol biosynthetic pathway have been isolated and characterized in S. cerevisiae. It is important that the homologues of the human fungal pathogen, C. albicans, are similarly investigated to determine whether they are essential since both organisms have demonstrated several differences as to which steps are required for growth and which are not. The C. albicans ERG27 gene encoding the sterol 3-keto reductase has been isolated by complementation of an erg27 strain of S. cerevisiae. The C. albicans ERG27 gene encodes a 349 amino acid protein that is 60% identical at the amino acid level to the S. cerevisiae ERG27 gene. Both copies of the C. albicans ERG27 gene have been disrupted with the second disruption being accomplished using an ERG27 heterozygote containing an integrated rescue cassette with a third copy of the gene under the control of the pMAL2 inducible promoter. The C. albicans erg27 strain was able to grow only under conditions where the pMAL2-ERG27 was induced indicating that the gene is essential in this organism. There are currently no reports on the regulation of genes involved in C-4 demethylation. To explore ERG27 regulation, strains containing mutations in the ERG2, ERG3 and ERG11 genes were generated. Previously described C. albicans mutants of ERG6 and ERG24 were also employed along with the inhibitors, itraconazole and zaragozic acid A, to characterize ERG27 expression using Northern analysis. Expression was increased 3-4-fold in an erg11 background, 2-3 fold in erg6 and erg24 backgrounds while lesser increases were noted in erg2 and erg3 backgrounds. Itraconazole increased ERG27 expression 10-fold while zaragozic acid A increased expression 5- fold. These results support other observations where blocks in the ergosterol pathway generally up-regulate the expression of pathway genes.
Full conference title:
The 15 th Congress of the International Society for Human and Animal Mycology
- ISHAM 15th (2003)