Practice question

Gel filtration separates native protein complexes by hydrodynamic size; co-elution suggests residence in same large complex but does not distinguish direct versus bridged association. Co-immunoprecipitation from lysates preserves multiprotein assemblies, confirming co-complex membership. Yeast two-hybrid tests binary, direct physical interaction inside nucleus because reporter activation requires intimate contact between bait and prey fusions independent of other yeast proteins. When protein B uniquely appears positive in two-hybrid while others co-purify only, it indicates B is the direct interactor contacting bait, while A, C, D likely associate via B.