CELL-SPECIFIC EXPRESSION OF HUMAN BETA-GALACTOSIDE ALPHA-2,6-SIALYTRANSFERASE TRANSCRIPTS DIFFERING IN THE 5' UNTRANSLATED REGION

In humans, two cDNAs have been isolated encoding beta-galactoside alpha2,6-sialyltransferase, differing only in part of the 5' untranslated region. Primer extension data show that the two cDNAs are near full-length clones. RNase protection analysis of different cell types showed that the transcript corresponding to the alpha2,6-sialyltransferase cDNA isolated from a B-cell library resided only in mature B cells. In contrast, the transcript corresponding to the alpha2,6-sialyltransferase cDNA isolated from a placenta library was found in all cells tested. Our results also indicate the existence of a third alpha2,6-sialyltransferase transcript in the hepatoma cell line HepG2. Mature B cells were found to express high amounts of alpha2,6-sialyltransferase mRNA, compared to other cell types tested, as shown by Northern blot analysis. Moreover there was an increased expression of beta-galactoside alpha2,6-sialyltransferase mRNA in activated B cells compared to resting B cells. In vitro transcription and translation of the cDNAs resulted in a protein of 45 kDa, but the transcripts were translated with different efficiency, suggesting a role for the 5' untranslated region in regulation of translation. We have also made an alpha2,6-sialyltransferase construct lacking the specific 5' regions of the two cDNAs. A transcript generated from this construct was translated more efficiently in vitro than the two alpha2,6-sialyltransferase cDNAs.