Specific polar localization of ribosomes in Bacillus subtilis depends on active transcription

The large subunit of ribosomes in Bacillus subtilis was tagged by generation of a fusion of ribosomal protein L1 to blue fluorescent protein (BFP). The fusion was fully active and localized around the nucleoids, predominantly close to the cell poles, in growing cells. However, in stationary phase cells, and in growing cells treated with rifampicin, L1-BFP was distributed throughout the cells, in contrast to cells treated with chloramphenicol, in which ribosomes still localized around nucleoids. These data show that specific localization of ribosomes is not due to nucleoid exclusion, but is a dynamic process due to active synthesis of RNA. Dual labelling of ribosomes and cold shock proteins (CSPs) tagged with green fluorescent protein (GFP) revealed colocalization of both protein classes. CSPs are implicated in coupling of transcription with translation and may bridge the spatial separation of ribosomes and nucleoid-associated RNA polymerase.