The integrated state of the rolling-circle plasmid pTB913 in the composite Bacillus plasmid pTB19. |
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Authors: | Linda Oskam Dirk J Hillenga Gerard Venema and Sierd Bron |
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Institution: | (1) Department of Genetics, Biological Centre, University of Groningen, Kerklaan 30, NL-9751 NN Haren, The Netherlands |
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Abstract: | Summary pTB19, a 27 kb plasmid originating from a thermophilic Bacillus species, contains integrated copies of two rolling-circle type plasmids on a 10.6 kb DNA fragment. In the present study we analysed the part of pTB19 that contains the rolling-circle plasmid pTB913 and the region in between the two rolling-circle plasmids. We show that, in the integrated state, pTB913 was flanked by a 55 by direct repeat that duplicated part of the replication initiation gene repB. Since repB was interrupted, the integrated pTB913 could not initiate rolling-circle replication. Autonomously replicating pTB913 was produced from pTB19, probably through recombination between the 55 by direct repeats; this was a rare event. Since the second integrated rolling-circle type plasmid also contained a non-functional replication initiation gene, replication of pT1319 must be controlled by the RepA determinant. Theta-type replication, controlled by RepA is likely to account for the high stability of pTB19. In between the two integrated rolling-circle plasmids was present an open reading frame (447 codons) which could encode a protein of unknown function. |
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Keywords: | Thermophilic Bacillus Plasmid replication Plasmid integration Structural instability Intramolecular recombination |
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