EVIDENCE FOR INHIBITION OF MYEF-2 BINDING TO MBP-PROMOTER BY MEF-1 PUR-ALPHA/

Myelin basic protein (MBP) is a major component of the myelin sheath w hose production is developmentally controlled during myelinogenesis. E arlier studies have indicated that programmed expression of the MBP ge ne is regulated at the level of transcription. Evidently, the MB1 regu latory motif located between nucleotides -14 to -50 plays an important role in transcription of the MBP promoter in both in vitro and in viv o systems. The MB1 element contains binding sites for the activator pr otein MEF-1/Pur alpha and the repressor protein MyEF-2. In this study we use bandshift assays with purified MEF-1/Pur alpha and MyEF-2 and d emonstrate that binding of MyEF-2 to its target sequence is inhibited by MEF-1/Pur alpha. Under similar conditions, MyEF-2 enhances the asso ciation of MEF-1/Pur alpha with MB1 DNA. MEF-1/Pur alpha binds to MB1 in mono-and dimeric forms. Inclusion of MyEF-2 in the binding reaction increases the dimeric association of MEF-1/Pur alpha with the MB1 seq uence. The use of MEF-1/Pur alpha variants in the bandshift assay sugg ests that two distinct regions of this protein may be involved in its binding to the MB1 sequences, and its ability to block MyEF-2 interact ion with the MB1 sequence. Based on previous studies on the programmed expression of MEF-1/Pur alpha and MyEF-2 during myelination and the c urrent findings on their interplay for binding to the MB1 motif, a mod el is proposed for their involvement in transcriptional regulation of the MBP gene during the course of brain development. (C) 1997 Wiley-Li ss, Inc.