A gene-type-specific enhancer regulates the carbamyl phosphate synthetase I promoter by cooperating with the proximal GAG activating element.
The rat carbamyl phosphate synthetase I gene is expressed in two cell types: hepatocytes and epithelial cells of the intestinal mucosa. The proximal promoter contains a single activating element, GAG, two repressor elements (sites I and III) and an anti-repressor element (site II). Although these elements together exhibit the potential for complex regulation, they are unable to confer tissue-specific promoter activity. Here we have identified a cell-type-specific enhancer that lies 10 kilobases upstream of the promoter. Unexpectedly, the enhancer also functioned in a gene-type-specific manner. The enhancer stimulated promoter activity exclusively through the proximal GAG element. Abrogation of GAG, either directly by mutation of GAG or indirectly by sites I and III repressors, abolished enhancer activation. Conversely, activation of the heterologous thymidine kinase promoter by the enhancer required the introduction of GAG. The requirement for GAG, therefore, functions to constrain the enhancer to a specific target promoter.
Goping
I S
IS
Department of Biochemistry, McGill University, Montreal, Quebec, Canada.
Lamontagne
S
S
Shore
G C
GC
Nguyen
M
M
D000818:Animals; D001483:Base Sequence; D002222:Carbamoyl-Phosphate Synthase (Ammonia) / Q000096:biosynthesis* / Q000235:genetics*; D002460:Cell Line; D004742:Enhancer Elements, Genetic; D004848:Epithelium / Q000201:enzymology; D005347:Fibroblasts; D015971:Gene Expression Regulation, Enzymologic; D015698:Genomic Library; D007413:Intestinal Mucosa / Q000201:enzymology; D008099:Liver / Q000201:enzymology; D008114:Liver Neoplasms, Experimental; D008156:Luciferases / Q000096:biosynthesis; D008969:Molecular Sequence Data; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis; D017384:Sequence Deletion; D013937:Thymidine Kinase / Q000235:genetics; D014162:Transfection; D014407:Tumor Cells, Cultured
D011994:Recombinant Proteins; D008156:Luciferases; D013937:Thymidine Kinase; D002222:Carbamoyl-Phosphate Synthase (Ammonia)