Organization of a Hybrid between Phage f1 and Plasmid pSC101

We have characterized the 200-nucleotide-long insertion found in f1 after segregation of a chimeric phage containing the genomes of f1 and pSC101 [Ohsumi, M., Vovis, G. F. & Zinder, N. D. (1978) Virology 89, 438-449]. The insertion in this novel f1 species, called f1′, is derived from pSC101 and has the potential to form an extended base-paired secondary structure, as determined by nucleotide sequence analysis. A five-nucleotide direct repeat, derived from f1 sequences, is present in f1′. The 200 additional nucleotides that are inserted into the DNA sequence coding for the carboxy terminus of f1 gene IV protein have generated a novel carboxy terminus for the f1′gene IV protein. In vitro transcription-translation studies demonstrate that a read-through protein can be expressed, as predicted from the f1′nucleotide sequence results. This 200-nucleotide-long sequence appears to be a transposable element found within pSC101 and is similar in sequence to the inverted repeat found in Tn3. Restriction enzyme analysis of the chimeric phage DNA, coupled with the nucleotide sequencing results, allows us to predict a structure for the genomic organization of this chimera.