Genomic structure and expression of human beta-1,4-galactosyltransferase.
We have cloned 60 kilobases of overlapping human genomic DNA comprising the complete coding sequence of the biosynthetic enzyme beta-1,4-galactosyltransferase (GalTase). The human locus spans greater than 50 kb of genomic DNA and shows an exon structure similar to the mouse gene. However, contrary to the mouse and bovine systems, which yield two distinct transcripts, RNA blotting and RNase protection analysis of human mRNA derived from HeLa cells reveal only a single transcript, corresponding to the "short" form of the mouse and bovine transcripts. Furthermore, Northern analysis on a panel of human cell lines of varying tissue origin and morphology shows GalTase expression levels to be highly variable, consistent with the notion that GalTase expression and consequent cell-specific differences in galactosylation are at least partially regulated at the transcriptional level.