-35 Sequence

Definition

The -35 sequence is a DNA sequence element that is part of the promoter region in prokaryotic genes. It is located approximately 35 base pairs upstream of the transcription start site and plays a crucial role in the initiation of transcription by RNA polymerase.

5 Must Know Facts For Your Next Test

1. The -35 sequence is a highly conserved DNA motif with the consensus sequence 'TTGACA' that is recognized by the sigma subunit of RNA polymerase.
2. The -35 sequence, along with the -10 sequence, helps to recruit and position the RNA polymerase complex at the transcription start site.
3. The distance between the -35 sequence and the transcription start site is crucial for efficient transcription initiation, as it allows the correct positioning of the RNA polymerase.
4. Mutations or alterations in the -35 sequence can significantly impact the strength and efficiency of the promoter, affecting the expression of the downstream gene.
5. The -35 sequence is a key element in the recognition and binding of RNA polymerase to the promoter, making it an essential component of transcriptional regulation in prokaryotes.

Review Questions

• Explain the role of the -35 sequence in the initiation of transcription in prokaryotic cells.
  • The -35 sequence is a highly conserved DNA motif that serves as a recognition site for the sigma subunit of RNA polymerase in prokaryotes. This sequence, located approximately 35 base pairs upstream of the transcription start site, helps to recruit and position the RNA polymerase complex at the promoter region, allowing for the efficient initiation of transcription. The -35 sequence, along with the -10 sequence, is crucial for the proper binding and orientation of the RNA polymerase, which is necessary for the transcription of the downstream gene.
• Describe the relationship between the -35 sequence and the transcription start site, and how this affects gene expression.
  • The distance between the -35 sequence and the transcription start site is a critical factor in the efficiency of transcription initiation. The optimal spacing between these two elements allows the RNA polymerase to properly bind and position itself at the promoter, facilitating the recruitment of the necessary transcription factors and the accurate initiation of mRNA synthesis. Alterations in this spacing, such as mutations or insertions/deletions in the DNA sequence, can significantly impact the strength and efficiency of the promoter, ultimately affecting the expression level of the downstream gene. The precise positioning of the -35 sequence relative to the transcription start site is, therefore, a key determinant of gene expression in prokaryotic systems.
• Analyze the potential consequences of mutations or changes in the -35 sequence on the regulation of gene expression in prokaryotes.
  • Mutations or other changes in the -35 sequence can have profound effects on the regulation of gene expression in prokaryotic cells. Since the -35 sequence is a critical recognition site for the RNA polymerase complex, any alterations to this DNA motif can disrupt the binding and positioning of the polymerase at the promoter. This can lead to a reduction or complete loss of transcription initiation, resulting in decreased expression of the downstream gene. Conversely, strengthening the -35 sequence by introducing mutations that better match the consensus 'TTGACA' motif can enhance promoter activity and increase the expression of the associated gene. Understanding the importance of the -35 sequence in transcriptional regulation is, therefore, essential for understanding and manipulating gene expression in prokaryotic organisms.

Related terms

Promoter: A DNA sequence that serves as a recognition site for RNA polymerase, allowing it to bind and initiate transcription of a gene.

Transcription Start Site (TSS): The specific nucleotide position on the DNA where the RNA polymerase begins synthesizing the messenger RNA (mRNA) molecule.

RNA Polymerase: The enzyme responsible for transcribing DNA into RNA, including messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).