FIGURE 1: Constructions of humanized S. cerevisiae strains for functional analysis. Homology and complementation between yeast and human genes have to be considered for developing reliable functional assays. (A) When a yeast orthologue exists, yeast strains can be manipulated by directly inserting the mutation in the nucleotide corresponding to the human gene. (B) Mutants of human or yeast orthologous genes can be expressed from a plasmid. (C) Mutants of human or yeast orthologous genes can be replaced with the human counterpart. (D) In the case of an essential gene, functional analysis has to be evaluated in heterozygosis expressing the wild type form of the gene from a plasmid and mutating the endogenous one, or mutating one of the two alleles in a diploid strain. (E) When no homology between the human and yeast gene has been identified, the human gene is expressed from a plasmid.