Bruhn Matthias, Schindler Daniel, Kemter Franziska S, Wiley Michael R, Chase Kitty, Koroleva Galina I, Palacios Gustavo, Sozhamannan Shanmuga, Waldminghaus Torsten
LOEWE Centre for Synthetic Microbiology-SYNMIKRO, Philipps-Universität Marburg, Marburg, Germany.
Manchester Institute of Biotechnology, The University of Manchester, Manchester, United Kingdom.
Front Microbiol. 2018 Nov 30;9:2932. doi: 10.3389/fmicb.2018.02932. eCollection 2018.
Chromosomal inheritance in bacteria usually entails bidirectional replication of a single chromosome from a single origin into two copies and subsequent partitioning of one copy each into daughter cells upon cell division. However, the human pathogen and other harbor two chromosomes, a large Chr1 and a small Chr2. Chr1 and Chr2 have different origins, an type origin and a P1 plasmid-type origin, respectively, driving the replication of respective chromosomes. Recently, we described naturally occurring exceptions to the two-chromosome rule of : i.e., Chr1 and Chr2 fused single chromosome strains, NSCV1 and NSCV2, in which both origins of replication are present. Using NSCV1 and NSCV2, here we tested whether two types of origins of replication can function simultaneously on the same chromosome or one or the other origin is silenced. We found that in NSCV1, both origins are active whereas in NSCV2 is silenced despite the fact that it is functional in an isolated context. The activity appears to be primarily determined by the copy number of the triggering site, which in turn is determined by its location with respect to and on the fused chromosome.
细菌中的染色体遗传通常涉及从单个起始点对单个染色体进行双向复制，形成两个拷贝，随后在细胞分裂时将每个拷贝分别分配到子细胞中。然而，人类病原体及其他一些（细菌）含有两条染色体，一条大的染色体1（Chr1）和一条小的染色体2（Chr2）。Chr1和Chr2有不同的起始点，分别是一种类型的起始点和P1质粒类型的起始点，驱动各自染色体的复制。最近，我们描述了（该细菌）两条染色体规则的自然发生的例外情况：即Chr1和Chr2融合的单染色体菌株NSCV1和NSCV2，其中两个复制起始点都存在。利用NSCV1和NSCV2，我们在此测试了两种类型的复制起始点是否能在同一染色体上同时发挥作用，或者其中一个或另一个起始点是否被沉默。我们发现，在NSCV1中，两个起始点都是活跃的，而在NSCV2中，（某个起始点）尽管在孤立的情况下是有功能的，但却被沉默了。（该起始点的）活性似乎主要由触发位点的拷贝数决定，而触发位点的拷贝数又由其在融合染色体上相对于（其他位点）的位置决定。
