A partial cDNA coding a prolein with all the characteristics of a typical P450 and with high homology (32-39% identity) to the fungal and mammalian CYP51s was isolated from a wheat cDNA library. Alignment of the protein with other P450 sequences revesied that it was missing its N-terminal membrane anchor. The corresponding coding sequences from 1) the yeast lanosterol 14-demethylase, 2) the sorghum obtusifoliol 14-demethylase, were linked to the partial wheat cDNA and both chimera were expressed in yeast. The ratio of obtisifoliol to lanosteroi demethylation was increased in membranes of transformed yeast compared to w.t. control. Higher P450 expression (x 2) and higher obtusifoliol demelhylase activity (x 1.5) were obtained with the plant/plant chimera. To remove interference of the endogenous sterol Jemethylase the yeast CYP51 gene was disrupted in the transformed strains. Disruption did not affect growth of yeast overexpressing plant CYP51. It enhanced accumulation of microsomal membranes and expression of the plant/plant chimera (x 12), so as to obtain 40 nmol (CYP51/L culture with CYP51 representing 1% of microsomal protein. This optimized expression system of the plant sterol 14-demethylase provides and excellent tool for detailed enzymologic and mechanistic studies, to lest activity of new herbicides and improve fungicides selectivity.