Long terminal repeat

Definition

Long terminal repeats (LTRs) are repeated DNA sequences found at both ends of certain types of retrotransposons and retroviruses, playing a crucial role in the integration and replication processes. These LTRs contain promoter elements that facilitate the transcription of adjacent genes and can influence genomic rearrangements through their recombination potential.

5 Must Know Facts For Your Next Test

1. LTRs are typically 100 to 600 base pairs long and are essential for the proper functioning of retroviral and retrotransposon genomes.
2. They contain essential elements such as promoters, enhancers, and polyadenylation signals, which are crucial for gene expression.
3. LTRs can facilitate homologous recombination, leading to genomic instability or the generation of new genetic variations.
4. In some instances, LTRs can lead to the formation of composite transposons, contributing to larger structural variations in the genome.
5. LTR retrotransposons make up a significant portion of many eukaryotic genomes, highlighting their importance in evolutionary biology and genome organization.

Review Questions

• How do long terminal repeats (LTRs) influence the integration and replication processes of retrotransposons?
  • Long terminal repeats (LTRs) provide essential sequences that include promoters and polyadenylation signals necessary for the transcription of adjacent genes. During replication, these LTRs help in the integration of retrotransposons into new genomic locations by providing the machinery required for reverse transcription. This not only facilitates efficient gene expression but also allows retrotransposons to propagate within the host genome, making them significant players in genetic variation.
• Discuss the role of LTRs in recombination events within the genome and their potential impact on genomic stability.
  • LTRs play a pivotal role in recombination events by providing homologous sequences that can facilitate crossover between different regions of DNA. This activity can lead to genomic rearrangements such as deletions, duplications, or even inversions. While such recombination can introduce genetic diversity, it also has the potential to cause genomic instability if not properly regulated, impacting cellular function and evolutionary outcomes.
• Evaluate the evolutionary significance of long terminal repeats in shaping eukaryotic genomes and their contribution to genetic diversity.
  • The evolutionary significance of long terminal repeats (LTRs) is profound as they are responsible for shaping eukaryotic genomes through their ability to facilitate transposition and recombination. As LTR retrotransposons replicate and integrate into various genomic locations, they contribute to structural variations that drive evolution. This activity increases genetic diversity within populations, allowing for adaptability to changing environments and leading to speciation events over time. Their prevalence in many eukaryotic lineages underscores their role as key contributors to evolutionary dynamics.

Related terms

Retrotransposon: A type of transposable element that replicates through an RNA intermediate, utilizing reverse transcription to integrate into new genomic locations.

Transposition: The process by which a segment of DNA moves from one location in the genome to another, often involving transposable elements such as LTRs.

Recombination: The genetic process where DNA sequences are rearranged, which can lead to genetic diversity and is essential for processes like meiosis and transposable element activity.