engleski

The genetics of linear bacterial chromosomes

Background and purpose: Streptomyces are the genetically best characterised bacteria which posses a linear chromosome. The chromosomes are 8 Mb in size. Linear plasmids are also common and can integrate into the linear chromosome or pick up chromosomal genes to form plasmid primes. DNA sequences near the chromosome ends can undergo deletions and amplifications. Streptomyces species are a good model for understanding the basis of DNA rearrangements specific for linear bacterial chromosomes. Materials and methods: Strains of S. rimosus R6 and S. lividans 66 were used. The structure of DNA rearrangements were analysed by restriction analysis and Southern hybridisation. Transfer of the plasmid SLP2 of S. lividans 66 was achieved using conjugation and transformation of protoplasts. Results and conclusions: Three integration events of the plasmid pPZG102 into the chromosome of S. rimosus were analysed. A model was proposed to explain the integration of plasmid sequences near the middle of chromosomes. It was shown that maintenance of the plasmid SLP2 of S. lividans 66 was dependent on sequences at or near the chromosome ends. A model was proposed to explain the generation of coupled DNA amplifications and deletions in Streptomyces species.

streptomyces; linear plasmid; plasmid integration; DNA amplification

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