Human N‐Acetylglucosaminyltransferase III Gene is Transcribed from Multiple Promoters

We have isolated cDNA clones for the human N‐acetylglucosaminyltransferase III (GlcNAc‐transferase III) gene. Two of them, H15 and H20, contain 5′ non‐coding regions that are totally different from each other except for 8 bp adjacent to the putative initiation codon. Analysis of one of the genomic cosmid clones containing the GlcNAc–transferase III coding region, Hug3, revealed that the 5′ non‐coding regions of H15 and H20 contain two and one exons, respectively, in addition to the exon containing the coding region (exon 1). These have arisen as the result of alternative splicing. The transcription‐initiation sites were determined by primer‐extension analysis and 5′‐rapid amplification of cDNA ends (RACE). Both H15‐specific and H20‐specific primers gave cDNAs longer than those expected from the lengths of H15 and H20, and a primer complementary to the region around the intron/exon junction near the putative initiation codon also gave distinct signals. Promoter activities of the 5′‐flanking regions of H15, H20 and exon 1 were measured in a human hepatoblastoma cell line, HuH‐6 cells by luciferase assays. The 5′‐flanking region of exon 1 was the most active, whilst that of H15 was several times less active, and that of H20 was inactive. Our study suggests that multiple promoters of the GlcNAc‐transferase III gene contribute to the complex regulation of this gene.