ParB spreading requires DNA bridging.
The parABS system is a widely employed mechanism for plasmid partitioning and chromosome segregation in bacteria. ParB binds to parS sites on plasmids and chromosomes and associates with broad regions of adjacent DNA, a phenomenon known as spreading. Although essential for ParB function, the mechanism of spreading remains poorly understood. Using single-molecule approaches, we discovered that Bacillus subtilis ParB (Spo0J) is able to trap DNA loops. Point mutants in Spo0J that disrupt DNA bridging are defective in spreading and recruitment of structural maintenance of chromosomes (SMC) condensin complexes in vivo. DNA bridging helps to explain how a limited number of Spo0J molecules per parS site (~20) can spread over many kilobases and suggests a mechanism by which ParB proteins could facilitate the loading of SMC complexes. We show that DNA bridging is a property of diverse ParB homologs, suggesting broad evolutionary conservation.
Department of Systems Biology, Harvard Medical School, Boston, Massachusetts 02115, USA; Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA;
Thomas G W
TG
Graham
Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts 02115, USA;
Xindan
X
Wang
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA; Harvard Biophysics Program, Harvard Medical School, Boston, Massachusetts 02115, USA.
Dan
D
Song
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA; Harvard Biophysics Program, Harvard Medical School, Boston, Massachusetts 02115, USA.
Candice M
CM
Etson
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA;
Antoine M
AM
van Oijen
Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts 02115, USA;
David Z
DZ
Rudner
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA;
Joseph J
JJ
Loparo
D001412:Bacillus subtilis / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism; D053144:Cell Nucleus Shape / Q000235:genetics; D019915:DNA Primase / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000378:metabolism*; D017354:Point Mutation; D011485:Protein Binding
D001426:Bacterial Proteins; D018797:Cell Cycle Proteins; D004269:DNA, Bacterial; C118650:SMC protein, Bacteria; D019915:DNA Primase
ParB; Spo0J; bacterial chromosome segregation; single-molecule fluorescence