CHARACTERIZATION OF THE 5-MEMBRANE PROTEIN, ENTACTIN(PRIME; END OF THE MOUSE ENT GENE ENCODING THE BASEMENT)

Entactin (Ent) is a 150-kDa basement membrane glycoprotein that forms a complex with laminin and also binds to type-IV collagen. For the ini tial characterization of the 5' end of the mouse Ent gene, we isolated genomic clones that encompass the first three exons of the gene. A 3. 5-kb EcoRI fragment at the 5' end of the gene was sequenced and shown to contain 1226 bp of the 5'-flanking DNA, the 260-bp first exon, and 2060 bp of the first intron. The second exon is separated from the fir st exon by an intron that spans greater than Is kb. The major transcri ption start point (tsp) was mapped to 35 nucleotides upstream from the translation start codon. The 5'-flanking DNA contains a putative TATA box, two CAAT boxes and two GC boxes. Nine potential AP-2- and two po tential AP-1-binding sites were found in the upstream region and the f irst intron. The first 248 bp of the promoter region are G+C rich, and they are 65% identical to the promoter of human Ent. Fragments of the 5'-flanking DNA linked to a reporter gene were shown to have promoter activity in transient transfection assays.