RNA Polymerase Core vs. RNA Polymerase Holoenzyme

Transcription involves transcribing DNA into RNA. While DNA forms the template, RNA is the transcript. Both the strands of DNA can be used as a template. For a gene, one strand is used. The process starts at the 3′ terminal of DNA. The RNA is transcribed in the 5′ to 3′ direction.

Transcription takes place in three stages –

  • Initiation
  • Elongation
  • Termination

RNA polymerase holoenzyme – bacterial RNA polymerase scanning DNA for a promoter sequence. The RNA polymerase holoenzyme is a multi-subunit complex.

Core enzymes comprise subunits of enzymes required for catalytic activity as seen in the core enzyme RNA polymerase. RNA polymerase enzyme is an example of the core enzyme with no sigma factor. The enzyme has 1 beta (β), 1 beta prime (β’), 2 alpha (α) and 1 omega (ω).

Holoenzymes, on the other hand, are a result of the core enzyme and the sigma unit coming together. The sigma factor is mainly responsible to make sure the bacterial RNA polymerase associates with the DNA in a stable way only to the promoters, not at other regions.

The main difference between RNA polymerase core and RNA polymerase holoenzyme is that the core is enzymes lacking the sigma factor, while the holoenzyme is enzymes comprising the sigma factor.

Key Differences between RNA Polymerase Core and RNA Polymerase Holoenzyme

The table below depicts the differences between RNA Polymerase Core and RNA Polymerase Holoenzyme.

RNA Polymerase Core

RNA Polymerase Holoenzyme

What it is

Enzymes lacking sigma factor

Enzymes with sigma factor

What is the molecular weight?

About 400 kDa

About 419-470 kDa


α2, β, β’, and ω

α2, β, β’, ω, and σ

Involved in which step of transcription?




In transcription, performs a catalytic function

In transcription, involved in initiation. It initiates RNA synthesis from the sigma 70 specific bacterial and the phage promoters

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