ISOLATION AND CHARACTERIZATION OF THE HUMAN DIACYLGLYCEROL KINASE GENE

The 80 kDa diacylglycerol kinase (DGK) is abundantly expressed in oligodendrocytes and lymphocytes but not to a detectable extent in other cells such as neurons and hepatocytes. As an initial attempt to delineate the mechanism of the transcriptional control of the DGK gene, we have cloned from a human genomic library a 22 kb genomic fragment. The genomic clone consists of the 5'-flanking region and 17 exons coding for approx. 53% of the total exons of human DGK, including those encoding EF- hand and zinc-finger regions. The translation initiation site is located in the second exon. S1 nuclease mapping and primer extension analysis of the human DGK mRNA identified a major transcription initiation site (position +1) at 264 bp upstream from the initiator ATG. In the 5'-flanking sequence we detected a single GC box at -35 but no canonical TATA and CAAT sequences. However, the sequence starting from the cap site (AGTTCCTGCCA) is very similar to the initiator element that specifies the transcription initiation site of some housekeeping genes. In addition, the 5'-upstream region contains several putative cis-elements. Jurkat and HepG2 cells were transfected with various 5'-deletion mutants of the upstream region fused to the structural gene of chloramphenicol acetyltransferase (CAT). The CAT assay revealed that among constructs containing up to 3.4 kb of the 5'-flanking region, a fragment of 263 bp from the transcription initiation site contains a basic promoter that is active in both types of cells. Moreover, the region between -263 and -850 contains a negative element that is active in HepG2 but not in Jurkat cells. This negative element may, at least in part, be responsible for the cell type-specific expression of the DGK gene.