GAP-43 is a highly conserved neuronal protein whose expression is spatially and temporally regulated. Because this regulation may occur, at least in part, at the level of transcription, we have begun to characterize the regions upstream of the GAP-43 transcription unit which direct its neuronal-specific expression. Functional analyses of GAP-43 promoter-reporter constructs have been performed in stably transfected cell lines, including PC12, C6 and RAT2. These data indicate that as little as 600 bp of GAP-43 5'-flanking DNA sequence directs the expression in a neuronal-specific manner. A shorter construct containing 230 bp of 5'-flanking DNA sequence defines a GAP-43 minimal promoter that is active in both neuronal and glial but not in non-neural cell lines. An upstream region, previously shown by other investigators to have promoter activity, was able to stimulate transcription when linked to the downstream minimal promoter. However, this upstream region was by itself unable to direct transcription of the reporting gene. In addition, we have demonstrated that two polypurine tracts within the 5'-flanking DNA sequence of the GAP-43 gene adopt a non-duplex configuration in plasmids, and, when studied in the context of chromosomal integration, these regions have a stimulatory effect on transcription.