A B-lymphocyte-specific high-turnover protein: constitutive expression in resting B cells and induction of synthesis in proliferating cells.

A basic B-cell-specific protein of 35,000 daltons (XM1) is expressed at a high rate--comparable to actin--in resting splenic B lymphocytes of various species. Splenic or thymic T cells or fibroblasts do not express this protein. Upon polyclonal stimulation of B lymphocytes or in proliferating B-lymphocyte-derived cell lines, the synthesis of XM1 is switched off, but it is reinduced by agents that arrest replication, such as mitomycin C, hydroxyurea, ultraviolet light or gamma irradiation. Induction of XM1 after mutagen treatment is fast; the synthesis is regulated on the level of transcription or RNA processing. XM1 is turned over with half-life of less than 2 hr. XM1 is glycosylated. From compartment analysis and Triton solubilization it appears that XM1 is bound to the nuclear membrane.