Which of the following is a pull-down tag?
Pull-down assays isolate interacting partners using affinity tags fused to bait protein. Glutathione S-transferase is a 26 kDa tag that binds with high affinity to immobilized glutathione on agarose or sepharose beads. GST-tagged bait is expressed recombinantly, captured on resin, then incubated with prey lysate. After washing, complexes are eluted using reduced glutathione. GST offers good solubility enhancement and simple purification. Unlike GFP which is fluorescent tracer and EDTA which is chelator, GST functions as both solubility and affinity handle.
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.