Explain the following findings: (1) Core RNA polymerase...

Name: Problem 1, Chapter 6: Molecular Biology
Uploaded: 2021-01-08T09:58:11-08:00
Duration: 1 min 12 s
Channel: Rashmi Sinha
Description: Explain the following findings: (1) Core RNA polymerase transcribes intact T4 phage DNA only weakly, whereas holoenzyme transcribes this template very well; but (2) core polymerase can transcribe calf thymus DNA about as well as the holoenzyme can.

Explain the following findings: (1) Core RNA polymerase transcribes intact T4 phage DNA only weakly, whereas holoenzyme transcribes this template very well; but (2) core polymerase can transcribe calf thymus DNA about as well as the holoenzyme can.

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Key Concepts

RNA Polymerase Core vs Holoenzyme

The RNA polymerase core enzyme is responsible for the catalytic process of RNA synthesis but lacks the necessary components for specific promoter recognition. In contrast, the holoenzyme, which is formed by the association of the core enzyme with a sigma factor, can recognize and bind to specific promoter sequences, thereby ensuring efficient initiation of transcription.

Sigma Factor and Promoter Recognition

The sigma factor is a key accessory protein that confers promoter specificity to the RNA polymerase by binding to conserved promoter elements. In the context of T4 phage DNA, the sigma factor is crucial because it directs the holoenzyme to the specific promoters present on the phage genome, which the core enzyme alone cannot effectively recognize.

Template DNA Characteristics and Transcription Efficiency

Different DNA templates have distinct promoter architectures that can influence the efficiency of transcription initiation. Calf thymus DNA contains promoter-like sequences that may be sufficient for the core enzyme to bind and initiate transcription, whereas the promoter elements in intact T4 phage DNA are more dependent on the sigma factor for recognition, leading to a marked difference in transcription efficiency between the core enzyme and the holoenzyme.

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