GENOMIC STRUCTURE AND PROMOTER ACTIVITY OF THE MOUSE POLYSIALIC ACID SYNTHASE GENE (MST8SIA-II) - BRAIN-SPECIFIC EXPRESSION FROM A TATA-LESS GC-RICH SEQUENCE

The mouse ST8Sia II (mST8Sia II/STX) gene encodes a neural cell adhesi on molecule-specific polysialic acid synthase whose expression is regu lated during the developmental stages of mouse brain, To elucidate the molecular mechanism by which the expression is tissue-specifically an d developmentally regulated, we isolated the complete genomic DNA and characterized the promoter of the gene for mST8Sia II, The gene encodi ng mST8Sia II was found to span about 80 kilobases and to be composed of six exons. Primer extension and S1 nuclease protection analyses rev ealed that the transcription started from 167 nucleotides upstream of the translational initiation site, Promoter analyses of the 5'-flankin g region of the mST8Sia II gene using a luciferase gene reporter syste m revealed strong promoter activity in retinoic acid-induced different iated P19 cells, which highly express the mST8Sia II gene, Deletion an alyses demonstrated that the minimal promoter activity detected for th e proximal region 325 base pairs upstream from the translational initi ation codon (-158 to +167) could be modulated by various sequences wit hin the 9.5-kilobase 5'-flanking region, The minimal promoter was embe dded in a GC-rich domain (74%, GC content), in which two Spl binding m otifs as well as a long purine-rich region were found, but it lacked T ATA and CAAT boxes, The positive regulatory region located between -15 9 and -659 contained two additional Sp1 binding motifs and a long pyri midine-rich region, We also found that the minimal promoter region of the mST8Sia II gene was sufficient for expression of a reporter gene i n mST8Sia II gene-expressing neural differentiated P19 cells but not i n nonexpressing ones, Thus the TATA-less GC-rich minimal promoter regi on of mST8Sia II probably controls the cell type-specific expression o f the mST8Sia II gene.