-35 sequence

Definition

The -35 sequence is a conserved DNA sequence found in prokaryotic promoters, located approximately 35 base pairs upstream from the transcription start site. It plays a crucial role in the initiation of transcription by providing a binding site for the sigma factor of RNA polymerase, facilitating the proper assembly of the transcription machinery at the promoter region. The presence and specific sequence of the -35 region are essential for effective gene expression in prokaryotes.

5 Must Know Facts For Your Next Test

1. The -35 sequence typically consists of a conserved hexameric sequence, often represented as 'TTGACA'.
2. In addition to the -35 sequence, prokaryotic promoters often include a -10 sequence, also known as the Pribnow box, which further aids in transcription initiation.
3. Mutations or variations in the -35 sequence can significantly impact the binding affinity of RNA polymerase and thus alter gene expression levels.
4. The proper alignment of both the -35 and -10 sequences is essential for the formation of a stable transcription complex.
5. Prokaryotic organisms, such as bacteria, rely heavily on the -35 sequence for accurate transcription initiation due to their simpler gene regulation mechanisms.

Review Questions

• How does the -35 sequence contribute to the efficiency of transcription initiation in prokaryotes?
  • The -35 sequence contributes to transcription initiation by serving as a specific binding site for the sigma factor of RNA polymerase. When RNA polymerase binds to this region, it helps position the enzyme correctly at the promoter, ensuring that transcription starts at the right location. This precise interaction is crucial for efficient gene expression, as any disruption can lead to decreased transcription levels.
• Compare and contrast the roles of the -35 sequence and sigma factors in prokaryotic transcription initiation.
  • The -35 sequence is a conserved DNA motif that serves as a recognition site for sigma factors, which are proteins that facilitate RNA polymerase's binding to promoters. While the -35 sequence provides structural support for accurate transcription initiation, sigma factors help in locating these promoters across various genes. Together, they form an essential partnership, where the sigma factor recognizes and binds to the -35 region to initiate RNA synthesis effectively.
• Evaluate how mutations in the -35 sequence might affect bacterial gene regulation and overall cellular function.
  • Mutations in the -35 sequence can lead to altered binding affinity for RNA polymerase, which may result in either reduced or increased transcription of downstream genes. Such changes can disrupt normal cellular functions by misregulating essential pathways and processes, potentially leading to insufficient production of necessary proteins or toxic overexpression. Consequently, these mutations can affect bacterial growth, adaptation, and survival in various environments, demonstrating how critical precise gene regulation is for cellular health.

Related terms

Promoter: A specific region of DNA that initiates transcription of a particular gene, containing conserved sequences like the -10 and -35 regions.

Sigma factor: A protein that binds to RNA polymerase and helps direct it to specific promoters in prokaryotic DNA during the initiation of transcription.

Transcription initiation: The process by which RNA polymerase binds to the promoter region of DNA and begins synthesizing RNA.