What is the Difference Between RNA Polymerase Core and Holoenzyme

The key difference between RNA polymerase core and holoenzyme is that RNA polymerase core is an enzyme that does not have a sigma factor, while RNA polymerase holoenzyme is an enzyme that consists of a sigma factor.

The transcription in bacteria is a process where a segment of bacterial DNA is copied into a newly synthesized mRNA strand with the use of an RNA polymerase enzyme. This process occurs in three main steps: initiation, elongation, and termination. The bacterial RNA polymerase is made up of 6 subunits. RNA polymerase core consists of β, β′,α2 and ω subunits. This RNA polymerase core transforms into holoenzyme when σ (sigma) factor is bound to the core enzyme. RNA polymerase core and holoenzyme are two forms of bacterial RNA polymerase enzyme.

CONTENTS

1. Overview and Key Difference
2. What is RNA Polymerase Core  
3. What is RNA Polymerase Holoenzyme
4. Similarities – RNA Polymerase Core and Holoenzyme
5. RNA Polymerase Core vs Holoenzyme in Tabular Form
6. Summary – RNA Polymerase Core vs Holoenzyme

What is RNA Polymerase Core?

RNA polymerase core is an enzyme involved in bacterial transcription that is free from the sigma factor. It consists of 5 subunits designated as β, β′,α2, and ω. This enzyme does not initiate specific transcription from bacterial and phage DNA promoters. This is because it does not recognize any specific bacterial or phage DNA promoters. However, this enzyme retains the ability to transcribe RNA from nonspecific initiation sequences. Moreover, the addition of the sigma factor to this enzyme allows the enzyme to initiate RNA synthesis from specific bacterial and phage promoters. The molecular weight of the RNA polymerase core enzyme is approximately 400 kDa.

The core enzyme contains catalytic properties of RNA polymerase. The α subunit is a homodimer that is 36.5 kDa in size. It is encoded by the rpoA gene. The functions of this subunit are RNAP assembly, interactions with DNA, and transcription factors for transcriptional regulation. Β subunit is 150.4 kDa in size. It is encoded by the rpoB gene. The functions of this subunit are DNA and RNA binding, RNA synthesis, NTP binding, RMP binding site, and σ factor binding. β′ subunit is 155 kDa in size, and it is encoded by the rpoC gene. The functions of this subunit are DNA binding, RNA synthesis, catalytic Mg²⁺ coordination, ppGpp binding site 1, and σ factor binding. Furthermore, the ω factor is 10.2 kDa in size and encoded by rpoZ gene. The function of ω factor is RNAP folding and ppGpp binding site 1.

What is RNA Polymerase Holoenzyme?

RNA polymerase holoenzyme is composed of a specific component known as sigma factor other than β, β′, α2, and ω subunits. Because of the sigma factor, RNA polymerase holoenzyme can recognize promoters. The sigma factor also aids in the correct placement of RNA polymerase holoenzyme and unwinding at the start site. Once the sigma factor performs its required and specific function, it dissociates from the RNA polymerase holoenzyme while the catalytic portion (β, β′, α2, and ω) of RNA polymerase remains in the DNA and continues transcription.

The number of sigma factors varies between bacterial species. E. coli has seven sigma factors. Moreover, sigma factors are distinguished by their characteristic molecular weights. For example, σ⁷⁰ is the sigma factor with a molecular weight of 70 kDa. Different sigma factors are utilized by bacteria under different environmental conditions. Examples of different σ factors include; σ¹⁹, σ²⁴, σ¹⁸, σ³², σ³⁸, and σ⁵⁴.

What are the Similarities Between RNA Polymerase Core and Holoenzyme?

• RNA polymerase core and holoenzyme are two forms of bacterial RNA polymerase enzyme.
• Both forms are involved in bacterial transcription.
• They have subunits.
• They are protein molecules made up of amino acids.

What is the Difference Between RNA Polymerase Core and Holoenzyme?

RNA polymerase core is an enzyme that does not have a sigma factor, while RNA polymerase holoenzyme is an enzyme that consists of a sigma factor. Thus, this is the key difference between RNA polymerase core and holoenzyme. Furthermore, the RNA polymerase core mainly participates in the elongation step of the transcription, while the RNA polymerase holoenzyme mainly catalyzes in the initiation step of the transcription.

The below infographic presents the differences between RNA polymerase core and holoenzyme in tabular form for side by side comparison.

Summary – RNA Polymerase Core vs Holoenzyme

Bacterial RNA polymerase is a multi-subunit DNA-dependent enzyme. It participates in the transcription of bacteria. It is the key enzyme of gene expression and a target of regulation. RNA polymerase core and holoenzyme are two forms of bacterial RNA polymerase enzyme. RNA polymerase core does not have a sigma factor, while RNA polymerase holoenzyme consists of a sigma factor. So, this summarizes the difference between RNA polymerase core and holoenzyme.

Reference:

1. Sutherland, Catherine, and Katsuhiko S Murakami. “An Introduction to the Structure and Function of the Catalytic Core Enzyme of Escherichia Coli RNA Polymerase.” EcoSal Plus, U.S. National Library of Medicine, Aug. 2018.
2. Bae, Brian, et al. “Structure of a Bacterial RNA Polymerase Holoenzyme Open Promoter Complex.” ELife, ELife Sciences Publications, Ltd, 8 Sept. 2015.

Image Courtesy:

1. “Bacterial RNA-polymerase structure 1HQM” By litvinanna – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “DNA Transcription cycle” By Amitsabhadiyaj – Own work (CC BY-SA 4.0) via Commons Wikimedia