Transcriptional Control of the Human Sodium-coupled Neutral Amino Acid Transporter System A Gene by Amino Acid Availability is Mediated by an Intronic Element

System A amino acid transporter (SNAT2) gene expression is up-regulated at the transcriptional level in response to amino acid deprivation. Functional analysis of genomic fragments 5' upstream of the transcription start site, for both human and mouse SNAT2 genes showed that these regions exhibit promoter activity, but were amino acid unresponsive. However, when the human and mouse constructs were extended to include intron 1, it was observed that the rate of transcription was increased following amino acid deprivation. Deletion analysis of the human gene identified an intron 1 sequence spanning 54 nucleotides that was sufficient for conferring amino acid-dependent regulation to a minimal SNAT2 promoter. Alignment of the corresponding region from the human, mouse, and rat genomes revealed three highly conserved sequences. From site-directed mutagenesis, it was concluded that one of these sites functions as an amino acid response element (AARE) to regulate transcription. The core sequence of this site is identical to the AARE in the human CHOP gene. The SNAT2 AARE, along with a nearby conserved CAAT box, has enhancer activity in that it functions in an orientation and position independent manner, and it confers regulated transcription to a heterologous promoter.