Transcription Termination in Prokaryotes: Videos & Practice Problems

In prokaryotes, transcription termination occurs via two main mechanisms: factor-dependent termination and rho-dependent termination. Factor-dependent termination involves the formation of a stem-loop structure in the mRNA, which causes the RNA polymerase to dissociate from the DNA, thereby terminating transcription. On the other hand, rho-dependent termination relies on the rho protein binding to a specific site on the mRNA, known as the rho site. This binding leads to the release of RNA polymerase from the DNA, completing the transcription process. Both mechanisms ensure the proper synthesis and regulation of messenger RNA in prokaryotic cells.

Factor-dependent termination in prokaryotes involves the formation of a stem-loop structure in the mRNA. This structure is created when the mRNA hydrogen bonds with itself, forming a loop. The formation of this stem-loop structure causes a change in the mRNA's conformation, which leads to the dissociation of RNA polymerase from the DNA. As a result, transcription is terminated, and the newly synthesized mRNA is released. This mechanism ensures that the transcription process is properly concluded, allowing the mRNA to be used for protein synthesis.

In rho-dependent termination, the rho protein plays a crucial role by binding to a specific site on the mRNA known as the rho site. Once bound, the rho protein moves along the mRNA towards the RNA polymerase. This interaction causes the RNA polymerase to dissociate from the DNA, thereby terminating transcription. The rho protein's ability to bind and move along the mRNA is essential for the proper regulation and completion of the transcription process in prokaryotic cells.

The stem-loop structure in factor-dependent termination is significant because it induces the termination of transcription. This structure forms when the mRNA hydrogen bonds with itself, creating a loop. The formation of the stem-loop causes a conformational change in the mRNA, which leads to the dissociation of RNA polymerase from the DNA. This dissociation effectively ends the transcription process, ensuring that the mRNA is properly synthesized and ready for translation. The stem-loop structure is thus a critical element in the regulation of gene expression in prokaryotes.

Rho-dependent termination differs from factor-dependent termination in its reliance on the rho protein. In rho-dependent termination, the rho protein binds to a specific site on the mRNA, known as the rho site, and moves along the mRNA towards the RNA polymerase. This interaction causes the RNA polymerase to dissociate from the DNA, terminating transcription. In contrast, factor-dependent termination involves the formation of a stem-loop structure in the mRNA, which causes the RNA polymerase to dissociate from the DNA. Both mechanisms ensure the proper termination of transcription but utilize different processes to achieve this goal.