Which selectable marker suppresses yeast mutations?
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.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.