Distribution of a novel nuclear protein in normal and regenerating liver cells.

Monoclonal antibodies to a rat liver nuclear protein (B2, 68 kda, pI: 6.5-8.2) have been established and characterized to localize the distribution of this antigen in nuclear organization. It was demonstrated that this nuclear protein B2 is associated with actively transcribed nucleosomes and the nuclear matrix as revealed by immunogold labelling. In the regenerating liver cell, the immunogold particles are predominantly in the euchromatin as compared to the resting liver cells which are mainly in nuclear matrix and heterochromatin. It was also demonstrated that the incorporation of 32P into the nuclear protein B2 is increased 6-fold in the actively transcribed nucleosomes as compared to the nuclear matrix, as analyzed by two-dimensional polyacrylamide gel electrophoresis. We hypothesize that this nuclear protein may act as an anchorage point either for actively transcribed RNA or for DNA replication. Once this protein is highly phosphorylated, it dissociates from the nuclear envelope and can then dynamically interact with active nucleosomes within the nucleus.