Using in vitro recombinant DNA techniques, we have constructed a derivative of bacteriophage f1 which contains an amber mutation in the major coat protein gene (gene VIII) plus an additional wild-type copy of this gene in the intergenic space near the origin of phage DNA replication. The gene is functional in this new location and is expressed at the same level relative to available transcriptional template DNA (RF) as the corresponding gene in wild-type f1. The implication of this finding in terms of current models of gene expression in the filamentous coliphages is discussed. Intertypic mixing of coat protein monomers derived from the two genes occurs when this phage is grown in an amber suppressor host. The effect of this DNA insertion on replication of the f1 genome is discussed. The concept of restructuring the f1 genome as a means of studying its regulation and expression is also discussed.
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