Studies of the recognition sequence of phi X174 gene A protein. Cleavage site of phi X gene A protein in St-1 RFI DNA.

It is already known that phi X gene A protein converts besides phi X RFI DNA also the RFI DNAs of the single-stranded bacteriophages G4, St-1, alpha 3 and phi K into RFII DNA. We have extended this observations for bacteriophages G14 and U3. Restriction enzyme analysis placed the phi X gene A protein cleavage site in St-1 RF DNA in the HinfI restriction DNA fragment F10 and in the overlapping HaeIII restriction DNA fragment Z7. The exact position and the nucleotide sequence at the 3'-OH end of the nick were determined by DNA sequence analysis of the single-stranded DNA subfragment of the nicked DNA fragment F10 obtained by gelelectrophoresis in denaturing conditions. A stretch of 85 nucleotides of St-1 DNA around the position of the phi X gene A protein cleavage site was established by DNA sequence analysis of the restriction DNA fragment Z7F1. Comparison of this nucleotide sequence with the previously determined nucleotide sequence around the cleavage site of phi X gene A protein in phi X174 RF DNA and G4 RF DNA revealed an identical sequence of only 10 nucleotides. The results suggest that the recognition sequence of the phi X174 gene A protein lies within these 10 nucleotides.