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Gene Dosage as a Regulatory Factor for Gene Expression. I. In plac5-infected Cells

Department of Biology, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong>

To study the effect of gene dosage on gene expression, plac5cI857O29P3, 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 repressor is inactive. In measuring the synthesis of -galactosidase, it was possible to separate the effects of the lac promoter from those of the phage promoter. When the synthesis of -galactosidase was initiated from the inserted lac promoter in JC6256(⁺) in the presence of additional cyclic AMP, the rate and level of -galactosidase synthesis were directly proportional to the multiplicity of infection (gene dosage). Furthermore, -galactosidase synthesis was initiated about 5 min after infection, just as with isopropyl--D-thiogalactoside (IPTG) induction.

When the synthesis of -galactosidase was initiated from the phage promoter in JC6256 in the absence of additional cyclic AMP, the rate and level of -galactosidase synthesis were again linearly proportional to gene dosage. On the other hand, initiation of -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.

Keywords: gene dosage, lambda phage, -galactosidase, gene regulation

Received 13 April 1981; accepted 21 September 1981.