Identification of a cell type-specific silencer in the first exon of the His-1 gene

The His-1 gene is developmentally expressed in the murine choroid plexus bu t is silenced in the adult brain. To test the hypothesis that the gene cont ains cis-acting elements that contribute to this repression, we have analyz ed segments of the proximal promoter for negative regulatory sequences by t ransient transfection analysis. The activity of the proximal promoter was m oderately influenced by positively and negatively acting sequences located from -335 to -168 and -617 to -335, respectively A strong His-1-positive re gulatory element (HPRE, +18 to +29) was essential for maximal promoter acti vity and could also enhance the activity of the heterologous SV40 promoter in an orientation-dependent manner. The HPRE contains homology to the neuro nal restrictive silencer element (NRSE) but interacted with nuclear protein s that were distinct from the NRSE-binding factor (NRSF). By contrast, a po tent negative regulatory sequence (HNRE) was identified in the first exon t hat repressed either the His-1 or SV40 promoters by greater than 80%. This negative regulatory sequence interacted with nuclear proteins from cells th at contain a silent His-1 gene but showed no interaction with nuclear prote ins from cells that actively transcribe the endogenous gene. HNRE-mediated repression was orientation independent; most of this activity was mapped to a minimal 26-bp sequence. These findings suggest that the first exon of th e His-1 gene contains a cell type-specific silencer that contributes to the regulation of His-1 transcription. (C) 2000 Wiley-Liss, Inc.