72. The common feature of Rho-independent and Rho-dependent termination of transcription is:
1. the active signal lies in the direct repeats in nascent RNA
2. the active signal lies in double stranded DNA template
3. the active signal lies in nascent RNA
4. both require ATP
Introduction
In prokaryotic transcription, there are two mechanisms for terminating transcription: Rho-independent and Rho-dependent termination. Both mechanisms result in the release of the newly synthesized RNA from the DNA template. Despite their differences in the process, both share a common feature that is essential for the termination of transcription. Let’s explore this feature and understand the distinctions between the two mechanisms.
Rho-independent Termination
Rho-independent termination is also known as intrinsic termination. This mechanism relies on the formation of a hairpin loop in the RNA, followed by a sequence of uracil (U) residues. The formation of the hairpin causes the RNA polymerase to pause, and the weak U-A base pairs in the RNA-DNA hybrid facilitate the release of the RNA transcript.
Rho-dependent Termination
Rho-dependent termination involves the Rho protein, which is an RNA helicase. This protein binds to a specific rut (Rho utilization) site on the nascent RNA and moves along the RNA toward the RNA polymerase. When Rho reaches the RNA polymerase, it disrupts the RNA-DNA hybrid and releases the RNA molecule, thus terminating transcription.
Common Feature of Both Mechanisms
Both Rho-independent and Rho-dependent termination mechanisms rely on a key signal within the nascent RNA. In Rho-independent termination, this signal is the formation of a stable hairpin structure in the RNA, while in Rho-dependent termination, the signal is the rut site that Rho recognizes and binds to.
Thus, the common feature of both mechanisms is that the active signal lies in the nascent RNA. The Rho protein in Rho-dependent termination recognizes specific sequences in the nascent RNA, and in Rho-independent termination, the intrinsic sequence causes structural changes in the RNA that lead to termination.
Conclusion
The correct answer is:
3. the active signal lies in nascent RNA
Both Rho-independent and Rho-dependent termination mechanisms rely on signals within the nascent RNA, although the specific sequences and structures differ between the two types of termination.
