Functional characterization of a unique liver gene promoter.
Human phenylalanine hydroxylase (PAH) is specifically expressed in the liver to convert L-phenylalanine to L-tyrosine. Deficiency of the PAH enzyme causes classic phenylketonuria, a common genetic disorder. The human PAH gene has a TATA-less promoter with multiple transcriptional initiation sites. A 9-kilobase DNA fragment 5'-flanking to the human PAH gene is sufficient to confer tissue- and developmental stage-specific expression of a reporter gene in transgenic mice. Deletion studies showed that the -121-base pair proximal promoter still retained a significant level of activity in hepatic cells. At least two protein binding sites, PAH-A and PAH-B, were identified in the proximal region of the human PAH promoter using rat liver nuclear extract. The PAH-A site covers a unique palindromic sequence, and the PAH-B site contains CCCTCCC repeats. Both elements are ubiquitous and essential regulatory elements for transcriptional activity. Nuclear protein factors that bind to the PAH-A and -B sites are detected in different cell types and are distinct from previously characterized transcription factors. No tissue-specific transcription factor binding sites have been detected within the proximal promoter region of the human PAH gene. These results suggest that the PAH gene promoter has a unique organization of regulatory elements for its tissue-specific expression in comparison with other liver gene promoters.
Wang
Y
Y
Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas 77030.
Hahn
T M
TM
Tsai
S Y
SY
Woo
S L
SL
D001483:Base Sequence; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000378:metabolism; D006801:Humans; D008099:Liver / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000378:metabolism; D010651:Phenylalanine Hydroxylase / Q000235:genetics*; D011401:Promoter Regions, Genetic; D017384:Sequence Deletion; D013329:Structure-Activity Relationship
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D010651:Phenylalanine Hydroxylase