The monoclonal antibody LHC7.15 recognizes RNA-binding protein FUS also known as fusion (involved in t(12;16) in malignant liposarcoma) (TLS) and hnRPN P2. The antigen is differentially distributed between the nucleus and the cytoplasm in live and apoptotic cells. In late apoptotic cells, the antigen coalesces into aggregates that bleb from the cell surface. FUS is a multifunctional protein of 69 kD and binds DNA, RNA, and several known ribonucleoprotein autoantigens.The monoclonal antibody LHC7.15 binds nuclei in a speckled pattern reminiscent of the binding of anti-spliceosomal autoantibodies, and to sites in the cytoplasm of live cells. Upon induction of apoptosis, LHC7.15 binds intensely to nuclei before nuclear fragmentation, but is unreactive against nuclear fragments. In later stages of apoptosis, LHC7.15 binds large cytoplasmic granules that form near the plasma membrane, occupy a subset of surface blebs, and separate as apoptotic bodies from the remainder of the apoptotic cells.