Fertility inhibition gene of plasmid R100

The fin0 gene of R100 was isolated from the Fin0+ transducing phage VA lambda 57. The limits of the gene were determined by BAL31 digestions and by analysis of deletion mutations derived from an internal restriction site. The DNA sequence contained an open reading frame of 558 nucleotides that would encode a protein of 21,268 daltons. Synthesis of such a protein was observed only when the fragment was cloned in front of the TAC promoter. Deletions entering the large open reading frame from either end were Fin0-, while internal frame shift mutations retained high Fin0 activity. One such strain had a 13 bp internal deletion that would produce a protein of 63 amino acid residues of which 21 were basic. We were consequently unable to rigorously establish that the 558 base orf encoded a fin0 product. The strand opposite the large open reading frame contained several transcription termination signals, and it is possible that the active gene product is one or two small RNAs from this strand.