A reporter or tag knock-in cell models are engineered to express a reporter genelike a fluorescent protein (GFP, RFP, YFP) or a peptide tag like HA, or FLAG from an endogenous locus of interest. The reporter or tag can replace the gene of interest, can co-express from the same promoter, or be fused to the gene of interest. These cell models are useful for gene expression monitoring, co-protein purification, protein trafficking, drug screening, protein-protein interaction assay, and analyzing protein interactomes.