Characterization of regulatory sequences and nuclear factors that function in cooperation with the promoter of the human thymidylate synthase gene.

To identify the essential sequence of the promoter of the human thymidylate synthase (hTS) gene, deletion mutants were constructed and assayed for promoter activity. The essential sequence was located within 65 bp upstream from the major cap site and a sequence that reduces the promoter activity was found in a region upstream from the essential promoter sequence. We previously identified two DNA-binding nuclear factors, NF-TS2 and NF-TS3, that bind to a region around the site of initiation of translation of the hTS gene. In this study, we confirmed the binding site of these factors by gel mobility shift analysis and found that NF-TS2 is the major factor that binds to the hTS gene in HeLa cells, whereas NF-TS3 is the major factor in the TIG-1 line of human fibroblast cells. To clarify the function of these factors, we examined the effects of the binding of these factors on the promoter activity. Our findings suggest that the binding of NF-TS2 enhances the promoter activity of the hTS gene in HeLa cells, whereas the binding of NF-TS3 represses the activity of the same promoter in TIG-1 cells.