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Abstract:
DOUBLE-STRAND DNA replication of small single-stranded bacteriophages such as ΦX174 and filamentous phage fd is initiated by highly specific endonucleases. This was demonstrated in vitro with the isolation of ΦX cisA protein1 and more recently with that of fd gene II-protein2. Both endonucleases produce one single-strand break in the viral strand of superhelical RFI providing an origin for double-strand (ds) DNA replication3,4. For gene II-protein the strand specificity of nicking was demonstrated by cleavage of asymmetrically labelled fd RFI (viral strand 32P-labelled, complementary strand 3H-labelled) and subsequent alkaline sucrose sedimentation. As a result the viral strand was cleaved into a full length linear form, whereas the complementary strand remained circular (T.F.M. and K.G., submitted). Here we report the position of the nick in the nucleotide sequence of the fd genome.
