Expression of human chromosome 19p alpha(1,3)-fucosyltransferase genes in normal tissues. Alternative splicing, polyadenylation, and isoforms.

The human alpha(1,3)-fucosyltransferase genes FUT3, FUT5, and FUT6 form a cluster on chromosome 19p13.3. Expression was studied using reverse transcriptase-polymerase chain reaction, rapid amplification of cDNA ends, and Northern analyses. FUT3 and FUT6 were expressed at high levels, while FUT5 expression was lower and restricted to fewer cell types. Alternatively spliced transcripts were identified for FUT3 and FUT6 in kidney, liver, and colon. A 2.37-kilobase pair (kb) FUT3 transcript, detected at high levels in kidney and colon, was absent in liver. FUT6 expression was characterized by a 3.5-kb transcript present in kidney and liver, and a 2.5-kb transcript in colon and liver. Two polyadenylation sites were shown for FUT5, but absence of consensus sequences suggests reduced efficiency for cleavage and polyadenylation. Two polyadenylation sites were also shown for FUT6, with the alternatively spliced downstream signal in tissues expressing high levels of FUT6. In these tissues, additional splicing results in isoforms with catalytic domain deletions. No detectable alpha(1,3)- or alpha(1,4)-fucosyltransferase activity was found in assays of cells transfected with FUT6 isoform cDNAs. Thus, tissue-specific post-transcriptional modifications are associated with expression patterns of FUT3, FUT5, and FUT6.