Identification of a novel silencer that regulates the myelin basic protein gene in neural cells

The myelin basic protein gene produces two families of proteins, the golli proteins and the 'classic' myelin basic proteins from three transcription start sites (tsp). The golli proteins are expressed from the first tsp, and little is known about genetic elements that control its activity. We have examined elements that may regulate the expression of the golli products produced from this promoter in neural cell lines with constructs containing upstream portions of the first tsp by transient transfection assays. Three putative regulatory elements were identified, among them a 345bp novel silencer region, termed the golli silencer region (GSR), which was characterized in detail. This silencer was responsible for a significant (approx. 60%) inhibition of luciferase expression in PC12 cells. It was orientation-dependent and a double dose of this GSR completely abolished expression of the luciferase reporter activity. Transfections with deleted constructs identified three critical sites that bind at least two repressor proteins. We postulate that the silencer activity is the result of synergistic interactions between these repressor proteins and might involve the formation of a high-ordered protein-DNA structure.