G-Quadruplex-Enabling Sequence within the Human Tyrosine Hydroxylase Promoter Differentially Regulates Transcription

G-Quadruplexes (GQs) found within the promoter regions of genes are known to mostly act as repressors of transcription. Here we report a guanosine (G)-rich segment in the 3′-proximal promoter region of human tyrosine hydroxylase (TH), which acts as a necessary element for transcription. Tyrosine hydroxylase catalyzes the rate-limiting step in the catecholamine biosynthesis and is linked to several common neurological disorders such as Parkinson’s and schizophrenia. A 45 nucleotide (nt) sequence (wtTH49) within the human TH promoter contains multiple G-stretches that are extremely well conserved among the primates but deviate in rodents, which raises the possibility of variation in the GQ structures formed in the two orders with the potential for a distinctive functional outcome. Biochemical and biophysical studies, including single-molecule Forster resonance energy transfer, indicate that the wtTH49 sequence can adopt multiple GQ structures by using different combinations of G-stretches. A functional assa...