Rho-dependent and Rho-independent termination mechanisms are used to terminate RNA transcription, by interfering with the RNA polymerase.
Rho-dependent transcription termination involves the Rho protein binding to a specific sequence or motif on the transcript, spooling the transcript until it interacts with the polymerase, ceasing transcription. The spooling is caused by the ATPase activity of Rho, allowing it to wind the transcript around itself.
Rho-independent transcription termination does not require the Rho protein. Instead, the RNA transcript autonomously forms a GC-rich terminator stem-loop structure. This stem-loop structure interacts with the polymerase, causing it to stop transcription.
These two mechanisms for transcription termination can be modulated, such as with riboswitches. Riboswitches are able to respond to metabolite binding or terminator/anti-terminator binding, controlling premature termination of transcription. This can be used by the cell to regulate gene expression, modifying the number of successful transcripts that are synthesised.