Evidence for Direct Interactions between RNA Polymerase and Ribosomes.

Transcription and translation are coupled in prokaryotes. Coupling originates from close proximity of the RNA polymerase and the ribosome due to their concurrent binding to the same nascent RNA. A similar proximity between RNA polymerase and the ribosome occurs during ribosome biogenesis; when ribosome assembly ensues while the rRNA is being transcribed. Here we report the existence of direct physical interactions between RNA polymerase core enzyme and vacant ribosome in the absence of mediating factors. The interactions appear to be of ionic nature and persist in the presence of an excess of BSA, RNA, or phosphate. The binding of ribosomes to RNA polymerases saturates at a one to one stoichiometry, while that of RNA polymerase to ribosomes saturates at a two to one. The dissociation constant of these complexes is within the physiological concentration range of free RNA polymerase and ribosomes. When bound to ribosomes, the RNA polymerase adopts a conformation similar to that under high salt which appears...