University of Wroclaw, Faculty of Biotechnology, Laboratory of Molecular Microbiology, Wroclaw, Poland.
J Bacteriol. 2013 Oct;195(19):4445-55. doi: 10.1128/JB.00798-13. Epub 2013 Aug 2.
Streptomyces species are bacteria that resemble filamentous fungi in their hyphal mode of growth and sporulation. In Streptomyces coelicolor, the conversion of multigenomic aerial hyphae into chains of unigenomic spores requires synchronized septation accompanied by segregation of tens of chromosomes into prespore compartments. The chromosome segregation is dependent on ParB protein, which assembles into an array of nucleoprotein complexes in the aerial hyphae. Here, we report that nucleoprotein ParB complexes are bound in vitro and in vivo by topoisomerase I, TopA, which is the only topoisomerase I homolog found in S. coelicolor. TopA cannot be eliminated, and its depletion inhibits growth and blocks sporulation. Surprisingly, sporulation in the TopA-depleted strain could be partially restored by deletion of parB. Furthermore, the formation of regularly spaced ParB complexes, which is a prerequisite for proper chromosome segregation and septation during the development of aerial hyphae, has been found to depend on TopA. We hypothesize that TopA is recruited to ParB complexes during sporulation, and its activity is required to resolve segregating chromosomes.
链霉菌属的细菌在其菌丝生长和孢子形成方式上类似于丝状真菌。在变铅青链霉菌中，多基因组气生菌丝转化为单基因组孢子链需要伴随有数十个染色体分离到孢子隔室中的同步分隔。染色体的分离依赖于 ParB 蛋白，该蛋白在气生菌丝中组装成一系列核蛋白复合物。在这里，我们报告说拓扑异构酶 I（TopA）在体外和体内与核蛋白 ParB 复合物结合，TopA 是变铅青链霉菌中唯一发现的拓扑异构酶 I 同源物。不能消除 TopA，其缺失会抑制生长并阻断孢子形成。令人惊讶的是，TopA 缺失菌株的孢子形成可以通过缺失 parB 部分恢复。此外，规则间隔的 ParB 复合物的形成，这是气生菌丝发育过程中正确的染色体分离和分隔的前提条件，已经被发现依赖于 TopA。我们假设 TopA 在孢子形成过程中被招募到 ParB 复合物中，其活性是分离分离染色体所必需的。
