The 5'-flanking region of the synapsin I gene. A G+C-rich, TATA- and CAAT-less, phylogenetically conserved sequence with cell type-specific promoter function

Abstract

The 5'-terminal region of the rat gene for the neuron-specific phosphoprotein, synapsin I, was isolated and sequenced. It comprises 1472 nucleotides (nt) of 5'-flanking sequence, 507 nt of the first exon, and 242 nt of the first intron. A single transcription start site was mapped by primer extension and S1 nuclease analysis. A sequence of 340 nt upstream from the transcription start site and the first exon are G+C-rich and enriched in CpG dinucleotides, resembling a CpG island. The 5'-flanking sequence lacks TATA and CAAT consensus elements but contains a consensus motif for the cAMP-responsive element. Furthermore, we notice two potential consensus motifs which are also found in corresponding positions in the genes for the nerve growth factor receptor and the 68-kDa neurofilament protein. The 5'-terminal region of the human synapsin I gene was also cloned and sequenced. A high degree of sequence conservation between rat and human is found in the upstream 340 nt that coincides precisely with the G+C-rich domain and includes the consensus elements, and throughout the first exon including the untranslated sequence. Sequence conservation is also observed further upstream and at the beginning of the first intron. In a transient chloramphenicol acetyltransferase expression assay, 5'-flanking sequences of the rat synapsin I gene function as strong promoters in neuroblastoma cells, but not in fibroblastoid cells. 225 nt of 5'-flanking sequence and 105 nt of 5'-untranslated sequence are sufficient for cell-type specific transcription in this assay.