title: The replication of plastid minicircles involves rolling circle intermediates.
abstract: Plastid genomes of peridinin-containing dinoflagellates are unique in that its genes are found on multiple circular DNA molecules known as 'minicircles' of approximately 2-3 kb in size, carrying from one to three genes. The non-coding regions (NCRs) of these minicircles share a conserved core region (250-500 bp) that are AT-rich and have several inverted or direct repeats. Southern blot analysis using an NCR probe, after resolving a dinoflagellate whole DNA extract in pulsed-field gel electrophoresis (PFGE), revealed additional positive bands (APBs) of 6-8 kb in size. APBs preferentially diminished from cells treated with the DNA-replication inhibitor aphidicolin, when compared with 2-3 kb minicircles, implicating they are not large minicircles. The APBs are also exonuclease III-sensitive, implicating the presence of linear DNA. These properties and the migration pattern of the APBs in a 2D-gel electrophoresis were in agreement with a rolling circle type of replication, rather than the bubble-forming type. Atomic force microscopy of 6-8 kb DNA separated by PFGE revealed DNA intermediates with rolling circle shapes. Accumulating data thus supports the involvement of rolling circle intermediates in the replication of the minicircles.
authors.affiliation: Department of Biology, Hong Kong University of Science and Technology, Kowloon, Hong Kong SAR, PR China.
authors.forename: Siu Kai
authors.initials: SK
authors.lastname: Leung
authors.forename: Joseph T Y
authors.initials: JT
authors.lastname: Wong
mesh_terms: D000818:Animals; D016590:Aphidicolin / Q000494:pharmacology; D004261:DNA Replication; D043864:DNA, Catenated / Q000737:chemistry; D004270:DNA, Circular / Q000096:biosynthesis* / Q000737:chemistry / Q000648:ultrastructure; D016054:DNA, Protozoan / Q000096:biosynthesis* / Q000737:chemistry / Q000648:ultrastructure; D004141:Dinoflagellida / Q000235:genetics*; D016521:Electrophoresis, Gel, Pulsed-Field; D004791:Enzyme Inhibitors / Q000494:pharmacology; D054627:Genome, Plastid; D018625:Microscopy, Atomic Force
chemical_list: D043864:DNA, Catenated; D004270:DNA, Circular; D016054:DNA, Protozoan; D004791:Enzyme Inhibitors; D016590:Aphidicolin