(A) HEK 293T cell lines bearing epitope tag knock-ins (KI) to a genomic copy of the indicated microprotein/alt-protein coding sequence were subjected to immunofluorescence with anti-FLAG tag (magenta), colocalization marker for each indicated (sub)nuclear region (yellow, see Methods), and DAPI (cyan). Scale bar, 10 μm. Data are representative of three biological replicates. (B-E) Volcano plot of proteins enriched by co-immunoprecipitation (co-IP) from microprotein/alt-protein FLAG tag KI cells (PD, pull-down) vs. wild-type control HEK 293T nuclear lysates with label-free quantiative (LFQ) proteomics (N = 3, biological replicates). Baits and candidate interaction partner proteins known to colocalize to the same subnuclear compartment are indicated and gene names are labeled.