title: Gene dosage as a regulatory factor for gene expression. I. In lambda plac5-infected cells.
abstract: To study the effect of gene dosage on gene expression, lambda plac5cI857O29P3, a replication defective lambda phage carrying part of the lac operon (containing the lac promotor, operator and z gene) in the b2 region was studied in Escherichia coli strain JC6256 where the lac operon is deleted and at a temperature where the lambda repressor is inactive. In measuring the synthesis of beta-galactosidase, it was possible to separate the effects of the lac promoter from those of the phage promoter. When the synthesis of beta-galactosidase was initiated from the inserted lac promoter in JC6256(lambda +) in the presence of additional cyclic AMP, the rate and level of beta-galactosidase synthesis were directly proportional to the multiplicity of infection (gene dosage). Furthermore, beta-galactosidase synthesis was initiated about 5 min after infection, just as with isopropyl-beta-D-thiogalactoside (IPTG) induction. When the synthesis of beta-galactosidase was initiated from the phage promoter in JC6256 in the absence of additional cyclic AMP, the rate and level of beta-galactosidase synthesis were again linearly proportional to gene dosage. On the other hand, initiation of beta-galactosidase synthesis was delayed until 10 to 20 min after infection. These results suggest that: (i) in the absence of negative controlling factors, the extent of gene expression is proportional to gene dosage; (ii) varying the gene dosage can be used to regulate gene expression.
mesh_terms: D010582:Bacteriophage lambda / Q000235:genetics*; D000242:Cyclic AMP / Q000494:pharmacology; D004926:Escherichia coli; D005786:Gene Expression Regulation; D005809:Genes, Regulator; D005814:Genes, Viral; D007763:Lac Operon; D001616:beta-Galactosidase / Q000096:biosynthesis
chemical_list: D000242:Cyclic AMP; D001616:beta-Galactosidase