Time-dependent Effects of Transcription- And Translation-Halting Drugs on the Spatial Distributions of the Escherichia Coli Chromosome and Ribosomes

Mol Microbiol. 2014 Nov;94(4):871-87. doi: 10.1111/mmi.12805. Epub 2014 Oct 22.

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Chromosomes, Bacterial / metabolism*
  • Escherichia coli / drug effects*
  • Optical Imaging
  • Protein Biosynthesis / drug effects*
  • Ribosomes / metabolism*
  • Single-Cell Analysis
  • Spatio-Temporal Analysis
  • Transcription, Genetic / drug effects*

Substances

  • Anti-Bacterial Agents