A 39-KD DNA-BINDING PROTEIN FROM MOUSE-BRAIN STIMULATES TRANSCRIPTIONOF MYELIN BASIC-PROTEIN GENE IN OLIGODENDROCYTIC CELLS

The MB1 regulatory sequence of the myelin basic protein (MBP) gene spa nning between nucleotides -14 to -50 with respect to the transcription start site is critical for cell type-specific transcription of the MB P gene, which encodes the major protein component of myelin sheath in cells derived from the central nervous system (CNS), This regulatory s equence has the ability to interact with a developmentally controlled DNA-binding protein from mouse brain that stimulates transcription of MBP promoter in an in vitro system (Haas, S., J. Gordon, and K. Khalil i, 1993, Mol. Cell. Biol. 13:3103-3112). Here, we report the purificat ion of a 39-kD protein from mouse brain tissue at the peak of myelinat ion and MBP production that binds to the MB1 regulatory motif, Followi ng partial amino acid sequence analysis, we have identified a compleme ntary DNA encoding a 39-kD DNA-binding protein called pur alpha. Expre ssion of pur alpha cDNA in the prokaryotic and eukaryotic cells result ed in the synthesis of a protein with characteristics similar to the p urified brain-derived 39-kD protein in band shift competition assays, Cotransfection of the recombinant pur alpha expressor plasmid with MBP promoter construct indicated that Pur alpha stimulates transcription of the MBP promoter in oligodendrocytic cells, and that the nucleotide sequence required for binding of the 39-kD Pur alpha to DNA within th e MB1 region is crucial for this activity, Moreover, transient express ion of Pur alpha caused elevation in the level of endogenous MBP RNA i n oligodendrocytic cells. Thus, Pur alpha, a sequence-specific DNA-bin ding protein upon binding to MB1 regulatory region may play a signific ant role in determining the cell type-specific expression of MBP in br ain.