title: Analysis of HeLa cell hypoxanthine phosphoribosyltransferase mutants and revertants by two-dimensional polyacrylamide gel electrophoresis: evidence for silent gene activation.
abstract: The spot corresponding to hypoxanthine phosphoribosyltransferase (HPRT; IMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.8) has been identified in two-dimensional polyacrylamide gels of HeLa cell extracts. This spot is absent in gels of 24 HPRT dificient mutants. A missense mutant displays a new HPRT spot at the same molecular weight but different isoelectric focusing position. Five independently isolated revertants of the missense mutant display spots corresponding to both the wild-type and mutant proteins indicating that they synthesize HPRT from two separate genes. If the missense protein is synthesized from a mutated form of the initially active HPRT gene, then wild-type HPRT protein in the revertants must be snythesized from a newly activated but prevously silent wild-type gene. The newly activated gene in the revertants of the missense mutation appears unstable producing a high frequency of spontaneous HPRT mutants.
mesh_terms: D004591:Electrophoresis, Polyacrylamide Gel; D000939:Epitopes; D005796:Genes; D006367:HeLa Cells / Q000201:enzymology*; D007041:Hypoxanthine Phosphoribosyltransferase / Q000032:analysis / Q000276:immunology / Q000378:metabolism*; D009154:Mutation
chemical_list: D000939:Epitopes; D007041:Hypoxanthine Phosphoribosyltransferase