Linear molecules of tobacco ptDNA end at known replication origins and additional loci
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Higher plant plastid DNA (ptDNA) is generally described as a double-stranded circular molecule of the size of the monomer of the plastid genome. Also, the substrates and products of ptDNA replication are generally assumed to be circular molecules. Linear or partly linear ptDNA molecules were detected in our present study using pulsed-field gel electrophoresis and Southern blotting of ptDNA restricted with ‘single cutter’ restriction enzymes. These linear DNA molecules show discrete end points which were mapped using appropriate probes. One possible explanation of discrete ends would be that they represent origins of replication. Indeed, some of the mapped ends correlate well with the known origins of replication of tobacco plastids, i.e. both of the oriA sequences and—less pronouncedly—with the oriB elements. Other ends correspond to replication origins that were described for Oenothera hookeri, Zea mays, Glycine max and Chlamydomonas reinhardtii, respectively, while some of the mapped ends were not described previously and␣might therefore represent additional origins of replication.
KeywordsReplication Chloroplast PFGE Tobacco Origin of replication Plastome
Inverted repeat in the plastome
Large single copy region in the plastome
Origin of replication
Pulsed-field gel electrophoresis
Small single copy region in the plastome
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The authors gratefully acknowledge the expert technical assistance of Stefan Kirchner, the suggestion of Arnold Bendich and Delaine Oldenburg to use pre-electrophoresis and the funding of this work by a grant of the Deutsche Forschungsgemeinschaft (Ko 632/14–1,2).
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