ASSOCIATION OF PUR-ALPHA WITH RNAS HOMOLOGOUS TO 7-SL DETERMINES ITS BINDING ABILITY TO THE MYELIN BASIC-PROTEIN PROMOTER DNA-SEQUENCE

Cell type and developmental stage expression of the myelin basic prote in (MBP) gene in mouse brain is regulated at the transcriptional level . Earlier studies from our laboratory have led to the identification o f a DNA binding protein from mouse brain, named Pur alpha, which inter acts with the MB1 regulatory motif of the MBP and stimulates its trans cription in glial cells. In this report, we demonstrate that a cellula r RNA, with significant homology to 7 SL RNA is associated with Pur al pha, Results from band shift competition studies indicate that Pur alp ha-associated RNA (PU-RNA), inhibits the interaction of immunopurified Pur alpha with the MB1 DNA sequence, Re suits from Northern blot stud ies indicated that PU-RNA is expressed during various stages of brain development. Of interest, this RNA was found in association with Pur a lpha that was produced in the mouse brain at the early stage of brain development. Results from Northwestern analysis using a PU-RNA probe i dentified the regions within Pur alpha that are important for Pur alph a/PU-RNA association. Production of Purer at the early stage of brain development and its association with PU-RNA at this stage, when Pur al pha exhibits poor binding ability to the MB1 DNA sequence, suggests th at PU-RNA may function as a co-factor that negatively regulates Pur al pha interaction with the MBP promoter sequence.