Identification of functional elements in the bidirectional promoter of themouse Nthl1 and Tsc2 genes

The gene of mammalian endonuclease III homologs (NTHL1/Nthl1), a DNA glycos ylase/AP lyase involved in base excision repair, lies immediately adjacent to one of the tuberous sclerosis disease-determining genes, TSC2/Tsc2, in a head-to-head orientation. To clarify the regulation of these divergent gen es, we studied the promoter activities of these transcription units by luci ferase assay using HeLa cells. We found that the short spacer sequence of 6 3 base pairs (bp) between the mouse Nthl1 and Tsc2 genes shows bidirectiona l promoter activity essential for the transcription of both genes, The 63-b p sequence is well conserved among several mammalian species and contains t wo Ets-transcription factor binding sites (EBSs) in opposite directions. An Ets-family protein in the HeLa nuclear extract specifically bound to eithe r EBSs. Mutation of the core motif of the EBS demonstrated that EBS positiv ely regulates transcription of both mNthl1 and mTsc2 genes, These EBSs had an additive effect on transcription, and each EBS functioned equally in bot h directions. (C) 2000 Academic Press.