To elucidate the mechanisms regulating expression of para , which encodes the major class of sodium channels in the Drosophila nervous system, we have tried to locate upstream cis -acting regulatory elements by mapping the transcriptional start site and analyzing the region immediately upstream of para in region 14D of the polytene chromosomes. From these studies, we have discovered that the region contains a cluster of neurally expressing genes. Here we report the molecular characterization of the genomic organization of the 14D region and the genes within this region, which are: calnexin ( Cnx ), actin related protein 14D ( Arpl4D ), calcineurin A 14D ( CnnAl4D ), and chromosome associated protein ( Cap ). The tight clustering of these genes, their neuronal expression patterns, and their potential functions related to expression, modulation, or regulation of sodium channels raise the possibility that these genes represent a functionally related group sharing some coordinate regulatory mechanism.
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