PubMed · 876396
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J A Subirana, L C Puigjaner. 1977-06-23. Circular superhelical DNA.. https://doi.org/10.1038/267727a0
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Mini-Tn10luxABcam/Ptac-ATS was constructed in order to develop a luciferase-transducing bacteriophage for detecting Escherichia coli O157:H7. The transposon was designed to deliver a 3.6-kb insertion that confers n-decanal-dependent bioluminescence and resistance to chloramphenicol and was constructed using mini-Tn10cam/Ptac-ATS in the plasmid pNK2884 and luxAB from Vibrio harveyi. PhiV10, a temperate bacteriophage infecting common phage types of Escherichia coli O157:H7, was mutagenized as a prophage in E. coli O157:H7 strain R508. PhiV10::luxABcamA1-23 was rescued from the strain by propagating it on a strain lacking the bacteriophage and the vector containing the transposon. The bacteriophage transduced n-decanal-dependent bioluminescence to E. coli O157:H7 strain R508 that was measurable approximately 1 h post infection.
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Rolling circle type DNA replication is initiated by introduction of a nick in the leading strand of the origin by the initiator protein, which in most cases binds covalently to the 5' end of the nick. In filamentous phage, however, such a covalent complex has not been detected. Using a suitable substrate and short reaction time, we show that filamentous phage initiator gpII forms a covalent complex with nicked DNA, which rapidly dissociates unless gpII is inactivated. A peptide-DNA complex was isolated from trypsin digest of the complex by ion-exchange column chromatography and gel filtration, and its peptide sequence was determined. The result indicated that gpII was linked to DNA by the tyrosine residue at position 197 from the N-terminus. The mutant protein in which this tyrosine was replaced by phenylalanine did not show any detectable activity to complement gene II amber mutant phage in vivo. In vitro, the mutant protein recognized the origin and bent DNA as well as the wild-type does, but failed to introduce a nick and to relax the superhelicity of cognate DNA.