AN EXTENSIVE REPEAT STRUCTURE DOWN-REGULATES HUMAN MONOAMINE-OXIDASE-A PROMOTER ACTIVITY INDEPENDENT OF AN INITIATOR-LIKE SEQUENCE

The 5' flanking sequence of the human monoamine oxidase A (MAO A) gene consists of an extensive repeat structure. Two 90-bp repeats (I and I I) were found in the core promoter (the 0.24-kb PvuII/DraII fragment), each containing two Spl binding sites. An additional six repeats were found, five of which (Ill-VII) were upstream and one (-I) downstream of the core promoter. Using transient transfection assay with a human growth hormone reporter gene, we found that the upstream repeating uni ts Ill-VII (in a 0.78-kb BamHI/DraII fragment) down-regulate core prom oter activity to 13 +/- 10% in a human glioma cell line(1242 MG) and 2 +/- 1% in a cervical carcinoma cell line (HeLa), respectively. The 0. 24-kb core promoter activity was taken as 100%. Addition of the initia tor (Inr)-like sequence to this 0.78-kb fragment (0.82-kb BamHI/-17 fr agment) still showed decreased promoter activity(10 +/- 9% in 1242 MG cells and 8 +/- 1% in HeLa cells). Thus, the upstream sequence down-re gulates promoter activity with or without the Inr-like sequence. When the Inr-like sequence was added to the core promoter (0.28-kb PvuII/-1 7 fragment), the promoter activity decreases significantly in both 124 2 MG (55 +/- 6%) and HeLa (60 +/- 10%) cells. These results suggest th at although the Inr-like sequence is present in the human MAO A promot er, it acts as a negative cis element instead of a transcription initi ator.