Double-strand cleavage and strand joining by the replication initiator protein of filamentous phage f1.
The replication initiator protein (gene II protein (gpII] of bacteriophage f1 is a multifunctional protein that plays central roles in initiation and termination of phage DNA replication. It introduces a nick at a specific site on the (+)-strand of supercoiled replicative form DNA. The 3'-hydroxyl end of the nick serves as the primer for (+)-strand rolling-circle replication. Upon completion of a round of synthesis, gpII cleaves and circulaizes the displaced single strand. When Mn2+ is included in the buffer instead of Mg2+, gpII cleaves both strands. In this paper, we investigate the mechanism of the Mn2+-dependent double-strand cleavage activity of gpII. This reaction, unlike nicking in the presence of Mg2+, does not require superhelicity. The reaction proceeds in two kinetic steps: first nicking of the (+)-strand, and then cleavage of the (-)-strand. The nucleotide sequence requirement for nicking is reduced compared to that in the presence of Mg2+. The product of the double-strand cleavage has an unusual structure. The left end is a telomere-like hairpin since the (+)- and (-)-strands are joined, as demonstrated by base sequencing. The right end has a onebase 3'-overhang. This reaction probably reflects the cleavage-joining activity of gpII in the termination event.
Greenstein
D
D
Rockefeller University, New York, New York 10021.
Horiuchi
K
K
D001483:Base Sequence; D003090:Coliphages / Q000378:metabolism*; D004261:DNA Replication; D004279:DNA, Viral / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D008345:Manganese / Q000494:pharmacology; D008969:Molecular Sequence Data; D010957:Plasmids; D015183:Restriction Mapping; D013379:Substrate Specificity; D014764:Viral Proteins / Q000378:metabolism*
C024013:DNA replication complex protein, Bacteriophage lambda; D004279:DNA, Viral; D014764:Viral Proteins; C488880:gene II protein, Enterobacteria phage f1; D008345:Manganese