(a) HPLC analysis of biotransformation assays. Chromatograms at 270 nm of extracts from yeast cultures, after 24 h substrate introduction: (i) biotransformation of cresol by yeasts overexpressing CYP619C3; (ii) biotransformation of m-hydroxybenzyl alcohol by yeasts overexpressing CYP619C2; and (iii) biotransformation of cresol by yeasts overexpressing CYP619C2. For both controls, genes were inserted in the non-coding direction into the pYES vector and transformed yeast cells were reacted with each substrate for 24 h. M-HyBzOH, m-hydroxybenzyl alcohol; G-OH, gentisyl alcohol; T-OH, toluquinol; mABs, milliabsorbance units. (b) Enzymic reactions catalysed by CYP619C2 and CYP619C3, and their involvement in the hydroxylation steps of the patulin biosynthesis pathway. Dashed arrows represent the steps which occur upstream and downstream of steps catalysed by CYP619C2 and CYP619C3.