Bacillus subtilis SMC complexes juxtapose chromosome arms as they travel from origin to terminus.
Structural maintenance of chromosomes (SMC) complexes play critical roles in chromosome dynamics in virtually all organisms, but how they function remains poorly understood. In the bacterium Bacillus subtilis, SMC-condensin complexes are topologically loaded at centromeric sites adjacent to the replication origin. Here we provide evidence that these ring-shaped assemblies tether the left and right chromosome arms together while traveling from the origin to the terminus (>2 megabases) at rates >50 kilobases per minute. Condensin movement scales linearly with time, providing evidence for an active transport mechanism. These data support a model in which SMC complexes function by processively enlarging DNA loops. Loop formation followed by processive enlargement provides a mechanism by which condensin complexes compact and resolve sister chromatids in mitosis and by which cohesin generates topologically associating domains during interphase.
Department of Microbiology and Immunobiology, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA. rudner@hms.harvard.edu xindan@indiana.edu.
Xindan
X
Wang
Graduate Program in Biophysics, Harvard University, Cambridge, MA 02138, USA.
Hugo B
HB
Brandão
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Tung B K
TB
Le
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.|Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Michael T
MT
Laub
Department of Microbiology and Immunobiology, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA. rudner@hms.harvard.edu xindan@indiana.edu.
David Z
DZ
Rudner
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D001412:Bacillus subtilis / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D020090:Chromosome Segregation; D002876:Chromosomes, Bacterial / Q000737:chemistry / Q000378:metabolism*; D004269:DNA, Bacterial / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000378:metabolism*
D001426:Bacterial Proteins; D018797:Cell Cycle Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D046912:Multiprotein Complexes; C118650:SMC protein, Bacteria; C108312:condensin complexes; D000251:Adenosine Triphosphatases