Transcription control elements of the rat neuronal nicotinic acetylcholine receptor subunit alpha 3.

1. In situ hybridization histochemistry has revealed that neuronal nicotinic acetylcholine receptor subunits are widely expressed in unique although overlapping patterns in the central and peripheral nervous systems. In addition, an intricate regulation of expression is apparent during development. This raises the question of the transcription control of these complex distributions. 2. An analysis of the transcription control elements of one nicotinic receptor subunit, alpha 3, which is expressed both in the central and peripheral nervous systems as well as in PC12 cells, is presented here. 3. Overlapping genomic clones containing the rat beta 4, alpha 3, and alpha 5 gene cluster were isolated and a restriction map of this region was constructed. 4. The transcription start sites of the alpha 3 gene were mapped by RNase protection experiments. Surprisingly, there is no consensus TATA box upstream of these sites. This is consistent with the finding of multiple initiation sites. 5. Functional assays were done in PC12 cells using the bacterial chloramphenicol acetyltransferase gene as a reporter gene. Several restriction fragments from the region located 5' and including the transcription start sites were shown to promote transcription of the reporter gene and thus contain at least part of the alpha 3 promoter. In addition, a region further upstream, within the beta 4 transcription unit, appears to reduce transcriptional activity and thus could be a silencer. 6. It is proposed that this putative silencer is a selective force in maintaining the tight linkage of these three genes.