Difference Between Rho Dependent and Rho Independent Termination

The key difference between Rho dependent and Rho independent termination is that in Rho dependent termination, Rho factor binds with the transcript and terminates transcription by breaking hydrogen bonds between the template and the transcript, while Rho independent termination terminates the transcription by producing a hairpin loop structure and then U rich region in the transcript.

Transcription is one of the two stages of gene expression. It is the process that produces an mRNA sequence from the genetic information hidden in the DNA sequence of the gene. Transcription takes place via three steps: initiation, elongation and termination. RNA polymerase enzyme binds to the promoter sequence of the gene and starts catalyzing the synthesis of the RNA strand. Until the terminator sequence is found, RNA polymerase adds nucleotides and builds the RNA strand. In prokaryotes, termination happens through two major termination strategies: Rho dependent termination and Rho independent termination. Rho factor is a protein which has helicase activity.

CONTENTS

1. Overview and Key Difference
2. What is Rho Dependent Termination
3. What is Rho Independent Termination
4. Similarities Between Rho Dependent and Rho Independent Termination
5. Side by Side Comparison – Rho Dependent vs Rho Independent Termination in Tabular Form
6. Summary

What is Rho Dependent Termination?

Rho dependent termination is one of the two types of transcription termination strategy occurring in prokaryotes. Rho factor is a protein which has helicase activity.

Figure 01: Rho Dependent Termination

Rho protein binds with the RNA transcript and moves along the RNA polymerase in 5’-3’ direction, encouraging the dissociation of hydrogen bonds between the DNA template and RNA transcript. When Rho factor reaches the transcription bubble, it pulls DNA/RNA hybrid apart and releases the transcript from the transcription bubble. When this occurs, it terminates the transcription.

What is Rho Independent Termination?

Rho independent termination is the second strategy which terminates prokaryotic transcription. Usually, a terminator region has an inverted repeat sequence. Immediately after the inverted repeat sequence, there is an Adenine rich region (AAAA). When RNA polymerase moves ahead, it produces an mRNA sequence. Since the two regions are complementary in the inverted repeat sequence region, it forms a hairpin loop structure due to hydrogen bonding. Next region will be the U rich region. Hairpin structure ceases the RNA polymerase activity.

Figure 02: Rho Independent Termination

Moreover, in the U rich regions, there are weak interactions between U bases of transcript and A bases of the template. These weak Adenine-Uracil bonds destabilize the DNA template and the RNA transcript and separate each other. In the end, transcript liberates from the transcription site.

What are the Similarities Between Rho Dependent and Rho Independent Termination?

• Rho dependent and Rho independent termination are two major termination strategies found in prokaryotes.
• Both forms release transcript from the DNA template to terminate the transcription.

What is the Difference Between Rho Dependent and Rho Independent Termination?

Rho dependent termination is mediated by a Rho protein while Rho independent termination occurs via the formation of a hairpin loop structure. So, this is the key difference between Rho dependent and Rho independent termination. Furthermore, Rho protein utilizes ATP energy while Rho independent termination does not involve Rho protein and does not utilize ATP energy. Therefore, this is also a significant difference between Rho dependent and Rho independent termination.

The below infographic shows more comparisons related to the difference between Rho dependent and Rho independent termination.

Summary –  Rho Dependent vs Rho Independent Termination

Rho dependent and Rho independent termination are the two main transcription termination mechanisms occurring in prokaryotes. A Rho protein is responsible for the transcription termination in Rho dependent termination. In contrast, Rho independent termination occurs via a formation of the hairpin loop structure. So, this is the key difference between Rho dependent and Rho independent termination.

Reference:

1. “Stages of Transcription.” Khan Academy, Available here.
2. “Intrinsic Termination.” Wikipedia, Wikimedia Foundation, 8 Feb. 2019, Available here.

Image Courtesy:

1. “Rho-dependent terminator” By Oalnafo1 – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Rho-independent terminator” By Ppgardne at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia

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