How is transcription termination generally signaled in prokaryotes?

In prokaryotes, transcription termination is primarily signaled by the presence of the rho factor, a protein that is essential for the termination of transcription in certain genes. The rho factor functions as a helicase that binds to the RNA transcript and moves along it in pursuit of the RNA polymerase. When the RNA polymerase encounters a terminator sequence, which typically includes a region that promotes the formation of a stable RNA hairpin followed by a poly-U stretch, transcription can terminate. If the RNA polymerase stalls at the terminator due to the formation of the hairpin, the rho factor will catch up and facilitate the release of the RNA from the RNA polymerase, leading to termination of transcription.

Other options, such as phosphorylation of the carboxy-terminal domain (CTD), formation of a complex with TFIIH, and binding of TATA-binding protein (TBP) to the promoter, are mechanisms involved in transcription regulation and initiation mainly in eukaryotic systems, rather than prokaryotic transcription termination. These processes are part of the more complex transcription machinery in eukaryotes, where multiple transcription factors and post-translational modifications are required for effective transcription initiation and termination.