Identification of a phosphoprotein in the nuclear matrix by monoclonal antibodies.

Previous work in this laboratory has established that a rat liver nuclear phosphoprotein (B2:Mr 68,000, pI 6.5-8.2) is associated with actively transcribed nucleosomes, as demonstrated by its preferential release after mild treatment with micrococcal nuclease. In the present report we provide further immunological evidence ('Western Blot' analysis, solid-phase radioimmunoassay and indirect immunofluorescence) that in addition establishes the presence of this phosphoprotein in the nuclear-matrix protein fraction. This paradoxical localization suggests that this phosphoprotein may function in two separate and distinct roles within the realm of nuclear organization.