C/EBPalpha and C/EBPbeta are persistently associated with the rat liver nuclear matrix throughout development and the acute phase response.

The partitioning of C/EBPalpha and C/EBPbeta on the nuclear matrix structure was examined during the different transcriptional activities accompanying liver development and the acute phase (AP) response. The presence of C/EBPalpha and C/EBPbeta was established on the nuclear matrix. Their relative concentrations on the matrix always reflected the developmental stage- and AP-related fluctuations observed in the nuclear extract. Thus, they progressively increased as development proceeded, whereas during the AP response, C/EBPalpha decreased and C/EBPbeta increased. In addition, the levels of both transcription factors were always notably higher in the nuclear matrix than in the extracts. We conclude that the observed changes and overall enrichment of the nuclear matrix with regulatory proteins is a reflection of the importance of such interactions for the in vivo functioning of C/EBP proteins.