Determination of the human SULT1C3 mRNA sequence in LS180 cells

Abstract

The human SULT1C subfamily consists of SULT1C2, SULT1C4, and one putative gene, SULT1C3, which has been identified by computational analysis of the human genome but has not been reported as expressed in any human tissue. An unusual feature of the predicted SULT1C3 gene is that it contains a duplication of the last two exons, with the upstream copies designated as exons 7a and 8a and the downstream copies designated as exons 7b and 8b. The NCBI reference sequence for SULT1C3 mRNA (NM_001008743) begins at the predicted translation start site, ends with exons 7b and 8b, and does not include exon 7a or 8a. We used primers corresponding to sequences in exons 6 and 7b to survey SULT1C3 expression in human tissues and amplified a largerthan‐expected RT‐PCR fragment from small and large intestinal mRNA as well as from LS180 human colorectal adenocarcinoma cells. The cloned fragment contained exons 7a and 8a in addition to the expected portion of exon 7b. We then used 5′‐and 3′‐RACE to determine the entire SULT1C3 mRNA sequence in LS180 cells. These analyses indicated that the SULT1C3 gene contains a non‐coding exon ~7.1 kb upstream of the first coding exon and that the major SULT1C3 transcript contains exons 7a and 8a rather than 7b and 8b. We conclude that SULT1C3 is expressed in human intestinal cells but that its 3′‐exons are not those indicated for the reference sequence. This work was supported by NIH grants HL050710 and ES005823.