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e coli

SysBioM Lecture Series – James Weisshaar

Event Details

When: September 23, 2015, 2:00 PM

Location: 3rd Floor Orchard View Room , Discovery Building

Contact: 608-316-4401, hstampfli@wisc.edu

James Weisshaar

James Weisshaar

Spatiotemporal Biology of Transcription and Translation in E. coli

Superresolution fluorescence microscopy has enabled us to locate and track single ribosomes (chromosomally expressed S2-mEos2), RNA polymerase copies (chromosomally expressed β’-mEos2), and DNA loci (ParB-XFP labeling) in live E. coli with spatial accuracy of σ ~ 30 nm and time resolution of 2-10 ms when needed. Ribosome-RNAP segregation is strong, arguing against co-transcriptional translation as the primary means of protein synthesis. Diffusion of both ribosomes and RNAP is heterogeneous. This enables us to distinguish translating 70S-polysomes from 30S subunits searching for translation initiation sites. We can also distinguish transcribing RNAP copies from those searching for transcription initiation sites. Time-dependent imaging of the DNA stain Sytox Orange after drug treatment indicates that on the 0-5 min timescale, both rifampicin and chloramphenicol induce nucleoid contraction. This corroborates the transertion hypothesis (co-transcriptional translation and simultaneous insertion of membrane proteins). The combination of these new experimental data with coarse-grained models of DNA-ribosome mixing suggest a picture in which expansion of the nucleoid by transertion is important for optimal cell function. The expanded nucleoid enables facile recycling of ribosomal subunits from ribosome-rich regions (where most translation occurs) to the nucleoids (where they can initiate co-transcriptional translation). At the same time, free polysomes are excluded from the nucleoids. The resulting spatial segregation may enhance overall growth rate by restricting the space within which RNAP searches for transcription initiation sites and ribosomal subunits search for translation initiation sites. This in turn may enhance overall growth rate.

All SysBioM (Systems Biology in Madison) sponsored talks take place on Wednesdays at 2 p.m in the 3rd floor Orchard View room of the Discovery Building. Talks are open to the public. Access to the room is via the elevator behind Aldo’s Cafe in the Northeast corner of the building.