Mutations in the J-F intercistronic region of bacteriophages phi X174 and G4 affect the regulation of gene expression.

The J-F intercistronic region of the genomes of bacteriophages phi X174 and G4 is transcribed but not translated. It contains the potential for a perfectly base-paired hairpin structure, which has been proposed to act as a terminator of transcription or as a regulatory region for mRNA turnover (or both). We measured phage-specific protein synthesis in mutants with modifications of the hairpin sequence and found a relative decrease in the expression of the upstream gene D as compared to the downstream genes F, G, and H in all mutants. The mutations also appeared to affect the efficiency of the gene F ribosome-binding site. These data strongly support the regulatory significance of the J-F intercistronic region and the putative hairpin structure therein.