Effects of transposition and deletion upon coat protein gene expression in bacteriophage f1

We have studied expression of the major coat (gene VIII) protein in vivo in cells infected with variant fl phage whose genomes had been restructured in vitro. This gene with its most proximal promoter and terminator behaves as an independent transcription unit: coat protein expression is unaffected by transposition of the gene to the intergenic space (IG) and is independent of orientation. Deletion of the DNA sequence (−35 region) upstream of the Pribnow box of the promoter for the transposed gene eliminates coat protein expression. The position and orientation of the transposed DNA within the IG can, however, have marked effects upon phage DNA replication. In mutants diploid for the coat protein gene, the kinetics of phage production are altered by both the level of DNA replication and the level of coat protein expression. In partial diploid mutant infections virions can be assembled from mixtures of wild-type fl and variant coat protein molecules in which amino acid polymorphisms occur near the amino terminus.