Yeast-enhanced green fluorescent protein (yEGFP): a reporter of gene expression in Candida albicans

The green fluorescent protein (GFP) of Aequorea victoria has been developed here as a reporter for gene expression and protein localization in Candida albicans. When wild-type (wt) GFP was expressed in C. albicans, it was not possible to detect fluorescence or a translation product for the wt protein. Since this was probably due in part to the presence of the non-canonical CTG serine codon in the Aequorea sequence, this codon was changed to the leucine codon TTG. C. albicans cells expressing this construct contained GFP mRNA but were non-fluorescent and contained no detectable translation product. Hence a codon-optimized GFP gene was constructed in which all of the 239 amino acids are encoded by optimal codons for C albicans. In this gene were also incorporated two previously identified mutations in the chromophore that increase GFP fluorescence. C. albicans cells expressing this yeast-enhanced GFP gene (yEGFP3) are fluorescent and contain GFP protein. yEGFP3 can be used as a versatile reporter of gene expression in C. albicans and Saccharomyces cerevisiae and the optimized GFP described here should have broad applications in these and other fungal species.