Enables K48-linked polyubiquitin modification-dependent protein binding activity and identical protein binding activity. Involved in cellular response to DNA damage stimulus; negative regulation of double-strand break repair via homologous recombination; and regulation of cellular catabolic process. Located in several cellular components, including autophagosome; nucleoplasm; and site of DNA damage. Part of protein-containing complex. Colocalizes with cytosolic proteasome complex and nuclear proteasome complex. [provided by Alliance of Genome Resources, Apr 2022]