%0 Journal Article %A Luk, Ka-Cheung %A Mark, Kai-Keung %T Gene Dosage as a Regulatory Factor for Gene Expression. I. In λplac5-infected Cells %D 1982 %J Journal of General Virology, %V 58 %N 2 %P 297-304 %@ 1465-2099 %R https://doi.org/10.1099/0022-1317-58-2-297 %K lambda phage %K gene dosage %K β-galactosidase %K gene regulation %I Microbiology Society, %X SUMMARY To study the effect of gene dosage on gene expression, λplac5cI857O29P3, a replication defective lambda phage carrying part of the lac operon (containing the lac promoter, 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 λ repressor is inactive. In measuring the synthesis of β-galactosidase, it was possible to separate the effects of the lac promoter from those of the phage promoter. When the synthesis of β-galactosidase was initiated from the inserted lac promoter in JC6256(λ+) in the presence of additional cyclic AMP, the rate and level of β-galactosidase synthesis were directly proportional to the multiplicity of infection (gene dosage). Furthermore, β-galactosidase synthesis was initiated about 5 min after infection, just as with isopropyl-β-d-thiogalactoside (IPTG) induction. When the synthesis of β-galactosidase was initiated from the phage promoter in JC6256 in the absence of additional cyclic AMP, the rate and level of β-galactosidase synthesis were again linearly proportional to gene dosage. On the other hand, initiation of β-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. %U https://www.microbiologyresearch.org/content/journal/jgv/10.1099/0022-1317-58-2-297