期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：15
页码：E1845-E1850
DOI：10.1073/pnas.1423746112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceBacteria carry large extrachromosomal circular DNA molecules, called plasmids, that contain specific genes causing virulence and drug resistance. An active molecular machine based on actin- or tubulin-like filaments ensures proper inheritance of these low-copy-number plasmids. Tubulin-like filaments are involved in the maintenance of virulence plasmids in pathogens such as Bacillus thuringiensis, Bacillus anthraxis, and Bacillus cereus. We discovered that filaments of tubulin-like TubZ protein and TubRC centromeric complexes, containing TubR protein and tubC DNA, encoded on plasmid pBtoxis, self-assemble into a prokaryotic minus end-tracking system. Filament depolymerization and processive TubRC binding to shrinking minus ends cause directed DNA motility, most likely through pulling forces. Segregation of DNA is a fundamental process during cell division. The mechanism of prokaryotic DNA segregation is largely unknown, but several low-copy-number plasmids encode cytomotive filament systems of the actin type and tubulin type important for plasmid inheritance. Of these cytomotive filaments, only actin-like systems are mechanistically well characterized. In contrast, the mechanism by which filaments of tubulin-like TubZ protein mediate DNA motility is unknown. To understand polymer-driven DNA transport, we reconstituted the filaments of TubZ protein (TubZ filaments) from Bacillus thuringiensis pBtoxis plasmid with their centromeric TubRC complexes containing adaptor protein TubR and tubC DNA. TubZ alone assembled into polar filaments, which annealed laterally and treadmilled. Using single-molecule imaging, we show that TubRC complexes were not pushed by filament polymerization; instead, they processively tracked shrinking, depolymerizing minus ends. Additionally, the TubRC complex nucleated TubZ filaments and allowed for treadmilling. Overall, our results indicate a pulling mechanism for DNA transport by the TubZRC system. The discovered minus end-tracking property of the TubRC complex expands the mechanistic diversity of the prokaryotic cytoskeleton.
关键词：cytoskeleton ; tubulin homologue ; DNA segregation
