title: Time-dependent effects of transcription- and translation-halting drugs on the spatial distributions of the Escherichia coli chromosome and ribosomes.
abstract: Previously observed effects of rifampicin and chloramphenicol indicate that transcription and translation activity strongly affect the coarse spatial organization of the bacterial cytoplasm. Single-cell, time-resolved, quantitative imaging of chromosome and ribosome spatial distributions and ribosome diffusion in live Escherichia coli provides insight into the underlying mechanisms. Monte Carlo simulations of model DNA-ribosome mixtures support a novel nucleoid-ribosome mixing hypothesis. In normal conditions, 70S-polysomes and the chromosomal DNA segregate, while 30S and 50S ribosomal subunits are able to penetrate the nucleoids. Growth conditions and drug treatments determine the partitioning of ribosomes into 70S-polysomes versus free 30S and 50S subunits. Entropic and excluded volume effects then dictate the resulting chromosome and ribosome spatial distributions. Direct observation of radial contraction of the nucleoids 0-5 min after treatment with either transcription- or translation-halting drugs supports the hypothesis that simultaneous transcription, translation, and insertion of proteins into the membrane ('transertion') exerts an expanding force on the chromosomal DNA. Breaking of the DNA-RNA polymerase-mRNA-ribosome-membrane chain in either of two ways causes similar nucleoid contraction on a similar timescale. We suggest that chromosomal expansion due to transertion enables co-transcriptional translation throughout the nucleoids.
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, WI, 53706, USA.
authors.forename: Somenath
authors.initials: S
authors.lastname: Bakshi
authors.forename: Heejun
authors.initials: H
authors.lastname: Choi
authors.forename: Jagannath
authors.initials: J
authors.lastname: Mondal
authors.forename: James C
authors.initials: JC
authors.lastname: Weisshaar
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002876:Chromosomes, Bacterial / Q000378:metabolism*; D004926:Escherichia coli / Q000187:drug effects*; D061848:Optical Imaging; D014176:Protein Biosynthesis / Q000187:drug effects*; D012270:Ribosomes / Q000378:metabolism*; D059010:Single-Cell Analysis; D062211:Spatio-Temporal Analysis; D014158:Transcription, Genetic / Q000187:drug effects*
chemical_list: D000900:Anti-Bacterial Agents