NOVEL HETEROGENEITY EXISTS IN THE 5'-UNTRANSLATED REGION OF THE BETA-GALACTOSIDE ALPHA-2,6-SIALYLTRANSFERASE MESSENGER-RNAS IN THE HUMAN B-LYMPHOBLASTOID CELL-LINE, LOUCKES

Multiple mRNA isoforms are generated from SIAT1, the gene encoding the beta-galactoside alpha 2,6-sialyltransferase (ST6Gal I, SiaT-1, ST6N, alpha 2,6ST). These isoforms are transcriptionally initiated from a n umber of physically distinct promoter regions. In human B-lymphocytic cells, two SIAT1 mRNA isoforms have been identified. In order to deter mine if additional SIAT1 mRNA isotypes exist, RNA from Louckes, a huma n cell Line with the mature B-phenotype, was subjected to 5'-RACE anal ysis. In addition to the two previously characterized mRNA forms. thre e additional SIAT1 mRNA forms were identified. The new mRNA isoforms i ncorporate novel sequence blocks into their 5'-UT regions. The data st rongly suggest that these novel sequence blocks originate from previou sly undocumented 5'-noncoding exons and are incorporated into mRNA by alternative splicing events and/or usage of additional transcriptional promoter regions. BLAST analysis reveals no similarity of these novel regions, Exons U, V, and W, to sequences in GenBank. The only excepti on is Exon V, which contains a portion of Alu, a repetitive element. T he data suggest that two of these novel mRNA isotypes are likely to be minor components. However, one form may contribute significantly to t he SIAT1 mRNA pool in Louckes cells. (C) 1996 Academic Press, Inc.