Spatial organization of the flow of genetic information in bacteria

Eukaryotic cells spatially organize mRNA processes such as translation and mRNA decay. Much less is clear in bacterial cells where the spatial distribution of mature mRNA remains ambiguous. Using a sensitive method based on quantitative fluorescence in situ hybridization, we show here that in Caulobacter crescentus and Escherichia coli , chromosomally expressed mRNAs largely display limited dispersion from their site of transcription during their lifetime. We estimate apparent diffusion coefficients at least two orders of magnitude lower than expected for freely diffusing mRNA, and provide evidence in C. crescentus that this mRNA localization restricts ribosomal mobility. Furthermore, C. crescentus RNase E appears associated with the DNA independently of its mRNA substrates. Collectively, our findings show that bacteria can spatially organize translation and, potentially, mRNA decay by using the chromosome layout as a template. This chromosome-centric organization has important implications for cellular physiology and for our understanding of gene expression in bacteria. Bacterial organization The lack of compartmentalization in membrane-enclosed compartments in bacteria makes it difficult to determine how mature messenger RNAs are distributed within the cell. Llopis et al . used fluorescence experiments — tricky because bacteria are so small — to follow mRNA dispersal after transcription. They found, surprisingly, that newly transcribed mRNAs showed limited diffusion; they speculate that the packed chromosomal material may itself act as a partition to separate translation from mRNA degradation. In bacteria, the lack of compartmentalization within membrane-enclosed compartments has made it difficult to determine how mature messenger RNAs are spatially distributed. Here the authors use fluorescence experiments in bacteria to follow mRNA dispersal after transcription. They find, surprisingly, that the newly transcribed mRNAs show limited diffusion, and speculate that the packed chromosomal material may itself act as a partition to separate translation from mRNA degradation.