Structural elements are in capital letters with the name of the corresponding feature underneath them. Underlined and in italics:

possible transmembrane helix. In bold and italics: alpha helices. Underlined: Beta-sheets. In white letters and highlighted in black: meander loop and Cys pocket. The asterisks (*) indicate the three totally conserved amino acids among cytochromes P450, and the exclamation points (!) show the amino acid variation found in the deduced CYP61 from different X. dendrorhous strains. The CYP61 gene mutation To study the function of the CYP61 gene in X. dendrorhous, mutant cyp61 – strains were generated. The wild-type strains UCD 67–385 and CBS 6938 were transformed with plasmid pBS-cyp61/Hyg, and strain AVHN2 was transformed #SRT1720 order randurls[1|1|,|CHEM1|]# with plasmid pBS-cyp61/Zeo. All transformations were performed with linearized plasmids as indicated in Figure  4. Through a double homologous recombination event, the donor DNA fragment containing the CYP61 gene find more interrupted by one of the two resistance markers replaced the CYP61 gene in the yeast chromosome. In this way, we obtained the transformant strains 385-cyp61 hph , CBS-cyp61 hph and Av2-cyp61 zeo (Table  2). The genotype modifications in the transformant strains were validated

by PCR reactions using specific primers for the CYP61 gene, zeocin or hygromycin B resistance cassettes (Table  1) and genomic DNA from the parental and transformant strains. The amplicons confirmed the CYP61 gene interruption (Figure  5). However, as strain UCD 67–385 is diploid [30] and we were able to detect a CYP61 wild-type allele, the resulting strain 385-cyp61 hph is heterozygous (385-CYP61/cyp61 hph ). For this reason, strain 385-CYP61/cyp61 hph was transformed with the linearized plasmid pBS-cyp61/Zeo obtaining the cyp61 – homozygote mutant strain 385-cyp61 hph tuclazepam /cyp61 zeo (Figure  5). The ploidy levels of strains CBS 6938 and AVHN2 are unknown; based on random mutagenesis experiments

and by transformation of carotenogenic genes performed at our laboratory [21, 31], we estimate that these strains are aneuploid. In these cases, the PCR-based genotype analysis determined that a unique CYP61 gene copy was mutated in strains CBS-cyp61 hph and Av2-cyp61 zeo (Figure  5), indicating that these strains are hemizygous, so a second transformation event was not necessary in these mutants. Interestingly, a clear difference in the color phenotype could be distinguished among all the cyp61 – mutants and their corresponding parental strains, indicating alterations in carotenoid biosynthesis (see below). Figure 4 Plasmids constructed in this work. In each plasmid illustration, relevant features for this work, such as endonuclease recognition sites and primer binding sites (thin arrows), are shown. Some elements of the original plasmid (pBluescript SK-) were kept and shown in gray. Plasmid pBS-gCyp61 harbors the genomic version of the CYP61 gene from X.