Spatial and Temporal Organization of Chromosome Duplication and Segregation in the Cyanobacterium Synechococcus elongatus PCC 7942
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| Authors: | Anna H Chen Bruno Afonso Pamela A Silver David F Savage |
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| Institution: | 1. Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America.; 2. Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States of America.; 3. Department of Molecular and Cell Biology and Department of Chemistry, University of California, Berkeley, California, United States of America.; Center for Genomic Regulation, Spain, |
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| Abstract: | The spatial and temporal control of chromosome duplication and segregation is crucial for proper cell division. While this process is well studied in eukaryotic and some prokaryotic organisms, relatively little is known about it in prokaryotic polyploids such as Synechococcus elongatus PCC 7942, which is known to possess one to eight copies of its single chromosome. Using a fluorescent repressor-operator system, S. elongatus chromosomes and chromosome replication forks were tagged and visualized. We found that chromosomal duplication is asynchronous and that the total number of chromosomes is correlated with cell length. Thus, replication is independent of cell cycle and coupled to cell growth. Replication events occur in a spatially random fashion. However, once assembled, replisomes move in a constrained manner. On the other hand, we found that segregation displays a striking spatial organization in some cells. Chromosomes transiently align along the major axis of the cell and timing of alignment was correlated to cell division. This mechanism likely contributes to the non-random segregation of chromosome copies to daughter cells. |
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