volume 8 Numb«r 91980 Nucleic Acids Research Studies of the recognition sequence of </>Xl 74 gene A protein. Cleavage site of tpX gene A protein in St-1 RFI DNA

It is already known that (JX gene A protein converts besides OX RFI DNA also the RFI DNAs of the single-stranded bacteriophages G't, St-1, a3 and 0K into RFII DNA. We have extended this observation for bacteriophages Glk and U3• Restriction enzyme analysis placed the 0X gene A protein cleavage site in St-1 RF DNA in the Hinf \ restriction DNA fragment F I Q and in the overlapping ffaelll restriction DNA fragment Zj. The exact position and the nucleotide se-quence at the 3'-0H end of the nick were determined by DNA sequence analysis of the single-stranded DNA subfragment of the nicked DNA fragment Fio obtain-ed by gelelectrophoresis in denaturing conditions. A s-tretch of 85 nucleoti-des of St-1 DNA around the position of the (JX 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 0X gene A protein in 0X17*1 RF DNA and G1) RF DNA revealed an identical sequence of only 10 nucleotides. The results suggest that the recognition sequence of the 0X171 * gene A protein lies within these 10 nucleotides