title: Regulation of sister chromosome cohesion by the replication fork tracking protein SeqA.
abstract: Analogously to chromosome cohesion in eukaryotes, newly replicated DNA in E. coli is held together by inter-sister linkages before partitioning into daughter nucleoids. In both cases, initial joining is apparently mediated by DNA catenation, in which replication-induced positive supercoils diffuse behind the fork, causing newly replicated duplexes to twist around each other. Type-II topoisomerase-catalyzed sister separation is delayed by the well-characterized cohesin complex in eukaryotes, but cohesion control in E. coli is not currently understood. We report that the abundant fork tracking protein SeqA is a strong positive regulator of cohesion, and is responsible for markedly prolonged cohesion observed at "snap" loci. Epistasis analysis suggests that SeqA stabilizes cohesion by antagonizing Topo IV-mediated sister resolution, and possibly also by a direct bridging mechanism. We show that variable cohesion observed along the E. coli chromosome is caused by differential SeqA binding, with oriC and snap loci binding disproportionally more SeqA. We propose that SeqA binding results in loose inter-duplex junctions that are resistant to Topo IV cleavage. Lastly, reducing cohesion by genetic manipulation of Topo IV or SeqA resulted in dramatically slowed sister locus separation and poor nucleoid partitioning, indicating that cohesion has a prominent role in chromosome segregation.
authors.affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Mohan C
authors.initials: MC
authors.lastname: Joshi
authors.forename: David
authors.initials: D
authors.lastname: Magnan
authors.forename: Timothy P
authors.initials: TP
authors.lastname: Montminy
authors.forename: Mark
authors.initials: M
authors.lastname: Lies
authors.forename: Nicholas
authors.initials: N
authors.lastname: Stepankiw
authors.forename: David
authors.initials: D
authors.lastname: Bates
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D020090:Chromosome Segregation; D002875:Chromosomes / Q000235:genetics*; D004261:DNA Replication / Q000235:genetics*; D027101:DNA Topoisomerase IV / Q000235:genetics* / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism; D051738:Origin Recognition Complex / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D012854:Sister Chromatid Exchange / Q000235:genetics
chemical_list: D001425:Bacterial Outer Membrane Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C114650:OriC chromosomal replication origin; D051738:Origin Recognition Complex; C089746:SeqA protein, E coli; D027101:DNA Topoisomerase IV; D004250:DNA Topoisomerases, Type II