THE NUCLEAR MATRIX PROTEIN NMP-1 IS THE TRANSCRIPTION FACTOR YY1

NMP-1 was initially identified as a nuclear matrix-associated DNA-binding factor that exhibits sequence-specific recognition for the site IV regulatory element of a histone H4 gene. This distal promoter domain is a nuclear matrix interaction site, In the present study, we show that NMP-1 is the multifunctional transcription factor YY1. Gelshift and Western blot analyses demonstrate that NMP-1 is immunoreactive with YY1 antibody, Furthermore, purified YY1 protein specifically recognizes site IV and reconstitutes the NMP-1 complex, Western blot and gel-shift analyses indicate that YY1 is present within the nuclear matrix, In situ immunofluorescence studies show that a significant fraction of YY1 is localized in the nuclear matrix, principally but not exclusively associated with residual nucleoli. Our results confirm that NMP-1/YY1 is a ubiquitous protein that is present in both human cells and in rat osteosarcoma ROS 17/2.8 cells. The finding that NMP-1 is identical to YY1 suggests that this transcriptional regulator may mediate gene-matrix interactions, Our results are consistent with the concept that the nuclear matrix: may functionally compartmentalize the eukaryotic nucleus to support regulation of gene expression.