title: Paradoxical regulation of human argininosuccinate synthetase cDNA minigene in opposition to endogenous gene: evidence for intragenic control sequences.
abstract: Human somatic cell variants resistant to the arginine analog, canavanine, express 200-fold increased levels of argininosuccinate synthetase (AS) mRNA as compared to parental cells. In this study we examined whether AS cDNA sequences contain cis-acting regulatory elements that are involved in the induction of AS mRNA in canavanine-resistant cells. Minigene constructs containing AS cDNA sequences under the transcriptional control of a viral promoter were stably transfected into the human squamous cell carcinoma line, RPMI 2650. Upon conversion of cells to canavanine-resistance, expression of the endogenous AS gene increased by two orders of magnitude as expected. Surprisingly, however, expression of AS cDNA minigenes decreased 10- to 15-fold in canavanine-resistant cell variants. The observed down-modulation of AS cDNA minigene expression was dependent upon a concomitant induction of the endogenous AS gene and not simply expression of the canavanine-resistant phenotype. This paradoxical regulation was specific for AS gene sequences since a minigene containing the neomycin-resistance gene in place of AS cDNA sequences failed to regulate. Furthermore, minigenes lacking a substantial portion of the AS cDNA also failed to exhibit the down-modulation. These findings suggest that expression of the human AS gene is regulated by a specific and limiting, positively-acting, trans-acting mechanism in canavanine-resistant cells and that exogenous AS cDNA (mRNA) sequences can compete for this mechanism.
authors.affiliation: Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor 48109-0606.
authors.forename: F M
authors.initials: FM
authors.lastname: Boyce
authors.forename: R J
authors.initials: RJ
authors.lastname: Pogulis
authors.forename: S O
authors.initials: SO
authors.lastname: Freytag
mesh_terms: D001124:Argininosuccinate Synthase / Q000235:genetics*; D002172:Canavanine / Q000494:pharmacology; D002460:Cell Line; D004247:DNA / Q000235:genetics; D004720:Endonucleases; D005786:Gene Expression Regulation; D006801:Humans; D008025:Ligases / Q000235:genetics*; D008957:Models, Genetic; D010957:Plasmids; D015719:Single-Strand Specific DNA and RNA Endonucleases; D014162:Transfection
chemical_list: D002172:Canavanine; D004247:DNA; D004720:Endonucleases; D015719:Single-Strand Specific DNA and RNA Endonucleases; D008025:Ligases; D001124:Argininosuccinate Synthase