A new look at the promoter of the human monoamine oxidase A gene: mapping transcription initiation sites and capacity to drive luciferase expression.

Monoamine oxidase (MAO) A (EC 1.4.3.4) oxidizes norepinephrine and serotonin and is expressed in a cell type-specific manner. Recent evidence that MAO A-deficient males in a large Dutch kindred suffer from mild mental retardation and occasional episodes of impulsive aggressive behavior makes it important to understand how the human MAO A promoter is regulated. Conventional primer extension analyses of MAO A mRNA in earlier studies predicted incorrect transcription initiation sites for the human MAO A promoter. Reverse transcription and polymerase chain reaction (PCR) readily detected MAO A mRNA initiated 5' to -135 bp but not 5' to -226 bp (5' to the ATG initiation codon). PCR-assisted primer extension and RNase protection assays reveal that most MAO A mRNA is initiated between -30 and -40, which resembles a eukaryotic initiator element. Depending on the tissue source, a minor, variable proportion of MAO A mRNAs is initiated more distally at approximately -95 and -136, within the more proximal of two 90-bp GC-rich tandem repeats. Genomic DNA segments spanning -4 to -200 and -465 or -935, but not -4 to -82, drive robust luciferase expression in mammalian cells. We conclude that (a) the primary transcription initiation site occurs at a putative initiator (lnr) element located between -30 and -40, with a minor, tissue-specific proportion of additional initiation near -95 and -136; and (b) MAO A-luciferase reporter constructs that contained all the known transcription initiation sites exhibited no evidence for inhibitory cis elements between -200 and at least -935. The apparent inhibitory activity previously reported for sequences 5' to the most proximal PvuII site may have resulted from the use of partial promoter constructs that omitted the putative lnr element.