Effect of poly(ADP-ribose) synthetase on the expression of MHC class II molecules.

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We have demonstrated that the high expression of poly (ADP-ribose) synthetase (PARS) caused the depression of MHC class II molecules. In B cell lines, which constitutively express the class II molecule, there are significant amounts of PARS.Thus, we attempted to detect a cell type-specific trans-acting factor which interacted with PARS and regulated the MHC class II gene.I.We constructed a fusion protein by using the automodification and DNA binding domains of PARS.We labeled nuclear proteins with ^<35>S-Met in B cells and macrophage cells and the ^<35>S-labeled nuclear proteins were incubated with the PARS-fusion protein. We detected a 45kDa and 35kDa binding partner for PARS in B cells.II.We prepared a probe DNA of human MHC class II genomic DNA in the region of DNase I hypersensitive site II(DHSII). We prepared nuclear proteins from class II-positive cells, class II-inducible cells and negative cells and analyzed them by South-western blotting by the use of the DHS II DNA probe. We detected a 35kDa nuclear protein which interacted with the DNA probe. Whether or not the DHS II-associated 35kDa protein interacts with PARS is still under investigation.