In this work, that was recently published in PNAS, we track fluorescently labeled ribosomal subunits in bacterial cells. We show that translating ribosomes move much slower than free subunits. More importantly, we show that it is only translating ribosomes that are excluded from the bacterial nucleoid, whereas free subunits have full access to the nucleoid. This finding is important because several gene-regulation mechanisms require that ribosomes are able to initiate translation as soon as the RNA polymerase has initiated transcription, and it has been difficult to reconcile such a requirement with the observation that ribosomes are nucleoid-excluded.

The intensity maps show the location of bound and free ribosomal subunits. Although the fully assembled ribosome is excluded from the nucleus, the small subunits have access and can initiate translation before the complex is translocated to the periphery.