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Isolation and characterization of the gene encoding 2,3-oxidosqualene-lanosterol cyclase from Saccharomyces cerevisiae

Shi, Z., Buntel, C.J., Griffin, J.H.
Proceedings of the National Academy of Sciences of the United States of America 1994 v.91 no.15 pp. 7370-7374
Saccharomyces cerevisiae, structural genes, isomerases, nucleotide sequences, amino acid sequences
The ERG7 gene encoding oxidosqualene-lanosterol cyclase [(S)-2,3-epoxysqualene mutase (cyclizing, lanosterol forming), EC] from Saccharomyces cerevisiae has been cloned by genetic complementation of a cyclase-deficient erg7 strain. The DNA sequence of this gene has been determined and found to contain an open reading frame of 2196 nt (including stop codon) that encodes a predicted protein of 731 amino adds. The predicted molecular mass of the S. cerevisiae cyclase, 83.4 kDa, is similar to the predicted masses of the oxidosqualene-lanosterol cyclase from Candida albicans and the oxidosqualene-cycloartenol cyclose from Arabidopsis thaliana, as well as to the molecular masses assigned to vertebrate oxidosqualene-lanosterol cyclases; however, it is substantially larger than the molecular mass assigned to purified S. cerevisiae cyclase. At the level of DNA and predicted amino acid sequences, the S. cerevisiae and C. albicans cyclases share 56% and 63% identity, respectively. Tryptophan and tyrosine residues are unusually abundant in the predicted amino acid sequences of (oxido)-squalene cyclases, leading to a hypothesis that electron-rich aromatic side chains from these residues are essential features of cyclase active sites.