Monoclonal nonspecific suppressor factor (MNSF) is a cytokine product of murine T cell  hybridoma that inhibits the generation of lipopolysaccharide-induced immunoglobulin secreting cells. MNSF is inducible with concanavalin A (Con A) and interferon-γ (IFN-γ). MNSFβ, a ubiquitin-like polypeptide (Ubi-L), is an effector molecule of MNSF. Here we give a description of the characteristics of Ubi-L and other ubiquitin-like proteins.