title: Bipolar localization of the group II intron Ll.LtrB is maintained in Escherichia coli deficient in nucleoid condensation, chromosome partitioning and DNA replication.
abstract: Group II introns are mobile genetic elements that invade their cognate intron-minus alleles via an RNA intermediate, in a process known as retrohoming. They can also retrotranspose to ectopic sites at low frequency. In Escherichia coli, retrotransposition of the lactococcal group II intron, Ll.LtrB, occurs preferentially within the Ori and Ter macrodomains of the E. coli chromosome. These macrodomains migrate towards the poles of the cell, where the intron-encoded protein, LtrA, localizes. Here we investigate whether alteration of nucleoid condensation, chromosome partitioning and replication affect retrotransposition frequencies, as well as bipolar localization of the Ll.LtrB intron integration and LtrA distribution in E. coli. We thus examined these properties in the absence of the nucleoid-associated proteins H-NS, StpA and MukB, in variants of partitioning functions including the centromere-like sequence migS and the actin homologue MreB, as well as in the replication mutants DeltaoriC, seqA, tus and topoIV (ts). Although there were some dramatic fluctuations in retrotransposition levels in these hosts, bipolar localization of integration events was maintained. LtrA was consistently found in nucleoid-free regions, with its localization to the cellular poles being largely preserved in these hosts. Together, these results suggest that bipolar localization of group II intron retrotransposition results from the residence of the intron-encoded protein at the poles of the cell.
authors.affiliation: Molecular Genetics Program, Wadsworth Center, New York State Department of Health, Center for Medical Sciences, 150 New Scotland Avenue, Albany, NY 12208, USA.
authors.forename: Arthur
authors.initials: A
authors.lastname: Beauregard
authors.forename: Venkata R
authors.initials: VR
authors.lastname: Chalamcharla
authors.forename: Carol Lyn
authors.initials: CL
authors.lastname: Piazza
authors.forename: Marlene
authors.initials: M
authors.lastname: Belfort
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Coros
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D022003:Cell Nucleus Structures / Q000235:genetics / Q000378:metabolism; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics; D020090:Chromosome Segregation; D002876:Chromosomes, Bacterial / Q000235:genetics; D004261:DNA Replication; D004251:DNA Transposable Elements / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000235:genetics; D007438:Introns; D018832:Molecular Chaperones / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D051738:Origin Recognition Complex; D012194:RNA-Directed DNA Polymerase / Q000235:genetics / Q000378:metabolism; D018626:Retroelements
chemical_list: D001426:Bacterial Proteins; D002868:Chromosomal Proteins, Non-Histone; D004251:DNA Transposable Elements; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C031908:H-NS protein, bacteria; C099786:LtrB protein, Lactococcus lactis; D018832:Molecular Chaperones; C067035:MukB protein, E coli; C114650:OriC chromosomal replication origin; D051738:Origin Recognition Complex; D018626:Retroelements; C090104:StpA protein, E coli; C099785:LtrA protein, Lactococcus lactis; D012194:RNA-Directed DNA Polymerase