MURINE HEPATIC BETA-GALACTOSIDE ALPHA-2,6-SIALYLTRANSFERASE GENE-EXPRESSION INVOLVES USAGE OF A NOVEL UPSTREAM EXON REGION

ST6Gal I (beta-galactoside alpha 2,6-sialyltransferase, SiaT-1, ST6N, EC 2.4.99.1) mediates the attachment of the alpha 2,6-sialyl linkage c ommon on N-linked glycans. Previous work suggests substantial inter-sp ecies conservation in SIAT1, the gene encoding ST6Gal I. In human and in rat, hepatic-specific SIAT1 transcription is initiated at Exon I. H ere we report a surprising departure in the structural organization of the murine ST6Gal I gene. By a combination of primer extension analys is, 5'-RACE analysis, and analysis of genomic sequences, we show that the murine hepatic ST6Gal I mRNA contains a novel region 5' of Exon I. This novel sequence is encoded oh a discrete upstream exon, Exon H. I n contrast to human and rat hepatic ST6Gal I, the murine mRNA is trans criptionally initiated at the start of Exon H. Differential mRNA blot analysis indicates that transcripts containing Exon H sequences are pr eferentially expressed in liver.