Alkaline phosphatase (AP) is expressed at high levels in all mineraliz
ing tissues, and the isoform identified in developing enamel has bioch
emical properties similar to that found in bone. While the bone AP is
referred to as the liver/bone/kidney or tissue non-specific (TNS) form
, other APs are highly specific for tissue of expression. To determine
unequivocally the AP isoform made by enamel organ cells, we construct
ed a fetal bovine enamel organ cDNA library, which yielded eight AP cD
NA clones. Tn each case, the DNA sequence was homologous to the partia
l cDNA reported for bovine kidney AF (Garattini et nl., 1987). It is c
oncluded that enamel organ cells express the TNS-AP isoform. The exten
ded 3' untranslated region of the cDNA has considerable homology to hu
man TNS-AP, and the conservation of sequence suggests that the 3' end
may have a role in post-transcriptional regulation of expression.