title: The stringent response and cell cycle arrest in Escherichia coli.
abstract: The bacterial stringent response, triggered by nutritional deprivation, causes an accumulation of the signaling nucleotides pppGpp and ppGpp. We characterize the replication arrest that occurs during the stringent response in Escherichia coli. Wild type cells undergo a RelA-dependent arrest after treatment with serine hydroxamate to contain an integer number of chromosomes and a replication origin-to-terminus ratio of 1. The growth rate prior to starvation determines the number of chromosomes upon arrest. Nucleoids of these cells are decondensed; in the absence of the ability to synthesize ppGpp, nucleoids become highly condensed, similar to that seen after treatment with the translational inhibitor chloramphenicol. After induction of the stringent response, while regions corresponding to the origins of replication segregate, the termini remain colocalized in wild-type cells. In contrast, cells arrested by rifampicin and cephalexin do not show colocalized termini, suggesting that the stringent response arrests chromosome segregation at a specific point. Release from starvation causes rapid nucleoid reorganization, chromosome segregation, and resumption of replication. Arrest of replication and inhibition of colony formation by ppGpp accumulation is relieved in seqA and dam mutants, although other aspects of the stringent response appear to be intact. We propose that DNA methylation and SeqA binding to non-origin loci is necessary to enforce a full stringent arrest, affecting both initiation of replication and chromosome segregation. This is the first indication that bacterial chromosome segregation, whose mechanism is not understood, is a step that may be regulated in response to environmental conditions.
authors.affiliation: Department of Biology and Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, MA, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Ferullo
authors.forename: Susan T
authors.initials: ST
authors.lastname: Lovett
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism; D002453:Cell Cycle; D020090:Chromosome Segregation; D002876:Chromosomes, Bacterial / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000166:cytology* / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D051738:Origin Recognition Complex / Q000235:genetics / Q000378:metabolism; D018741:Replication Origin; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific) / Q000235:genetics / Q000378:metabolism
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; C058693:Dam methyltransferase; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific)