Genomic organization of the murine polysialyltransferase gene ST8SiaIV (PST-1)

Polysialic acid (PSA) is an important regulator of cellular interactions. T wo enzymes (ST8SiaII and ST8SiaII) are capable of synthesizing PSA, In the present study, the gene encoding the murine ST8SiaIV (PST-1) has been isola ted and characterized. In contrast to the ST8SiaII (STX) gene which contain s six exons and spans about 80 kb, the ST8SiaIV gene comprises only five ex ons spanning over at least 55 kb, However, alignment of the two genes revea led that exon-intron boundaries of exons 2-5 of ST8SiaIV and exons 3-6 of S T8SiaII are located at identical sites. Differences are restricted to the 5 '-region encoded by one exon in the case of ST8SiaIV, whereas the correspon ding region of ST8SiaII is interrupted by a very long intron. 5'-RACE analy sis of the ST8SiaIV transcript using mRNA from AtT20 cells identified two t ranscription start sites at positions -324 and -204 relative to the transla tion start codon, The promoter region of ST8SiaIV lacks TATA- and CAAT-like sequences and is enriched in G+C (60%), The promoter contains putative Sp1 , AP-1, AP-2, and PEA3 binding sites, as well as a purine- and a pyrimidine -rich region. Luciferase reporter gene assays demonstrated that the region between nucleotides -443 and -162 is sufficient to direct gene expression. The induction of luciferase activity was 30- and 10-fold in the PSA-positiv e AtT20 and CHO cells, but only 5- and 7-fold in the PSA-negative NIH-3T3 c ells and in a PSA-negative subline of AtT20. Thus, although decreased in ac tivity in PSA-negative cell lines, the basal promoter is not sufficient for the strong cell-type and tissue specific regulation of the ST8SiaIV gene, suggesting regulatory elements in the more upstream 5'-region.