Practice question

In yeast genetics, suppressor tRNA markers are used to monitor nonsense mutation suppression. SUP4 encodes a tyrosine tRNA with anticodon mutated to recognize ochre stop codon UAA, suppressing ade2-101 and other ochre alleles, leading to phenotypic color change in adenine biosynthesis pathway. In YAC vectors, SUP4 is placed within cloning site; disruption by foreign DNA abolishes suppression. Auxotrophic markers URA3 and TRP1 provide selection for transformation, while LacZ and GFP are bacterial reporter genes. SUP4 thus acts as insertional marker that visibly reports insertion by altering suppression phenotype in yeast.