Evidence for inhibition of MyEF-2 binding to MBP promoter by MEF-1/Pur α

Myelin basic protein (MBP) is a major component of the myelin sheath whose production is developmentally controlled during myelinogenesis. Earlier studies have indicated that programmed expression of the MBP gene is regulated at the level of transcription. Evidently, the MB1 regulatory motif located between nucleotides −14 to −50 plays an important role in transcription of the MBP promoter in both in vitro and in vivo systems. The MB1 element contains binding sites for the activator protein MEF-1/Pur α and the repressor protein MyEF-2. In this study we use bandshift assays with purified MEF-1/Pur α and MyEF-2 and demonstrate that binding of MyEF-2 to its target sequence is inhibited by MEF-1/Pur α. Under similar conditions, MyEF-2 enhances the association of MEF-1/Pur α with MB1 DNA. MEF-1/Pur α binds to MB1 in mono- and dimeric forms. Inclusion of MyEF-2 in the binding reaction increases the dimeric association of MEF-1/Pur α with the MB1 sequence. The use of MEF-1/Pur α variants in the bandshift assay suggests that two distinct regions of this protein may be involved in its binding to the MB1 sequences, and its ability to block MyEF-2 interaction with the MB1 sequence. Based on previous studies on the programmed expression of MEF-1/Pur α and MyEF-2 during myelination and the current findings on their interplay for binding to the MB1 motif, a model is proposed for their involvement in transcriptional regulation of the MBP gene during the course of brain development. J. Cell. Biochem. 66:524–531, 1997. © 1997 Wiley-Liss, Inc.