Retroelement

Retroelement

A retroelement is a type of genetic element that can amplify itself in a genome through an RNA intermediate. Retroelements are a significant component of many eukaryotic genomes, including humans, where they contribute to genetic diversity and evolution. They are characterized by their ability to reverse transcribe RNA into DNA, a process facilitated by the enzyme reverse transcriptase.

Types of Retroelement

Retroelements can be broadly classified into two main categories:

1. Retrotransposons

Retrotransposons are genetic elements that can move around within the genome. They are further divided into two main types:

• Long Terminal Repeat (LTR) Retrotransposons: These elements are flanked by long terminal repeats and are similar in structure to retroviruses. They include endogenous retroviruses (ERVs) and are capable of autonomous replication.

• Non-Long Terminal Repeat (Non-LTR) Retrotransposons: These lack LTRs and include:

 * LINEs (Long Interspersed Nuclear Elements): Autonomous elements that encode the proteins necessary for their own retrotransposition.
 * SINEs (Short Interspersed Nuclear Elements): Non-autonomous elements that rely on the machinery of LINEs for their propagation.

2. Retrogenes

Retrogenes are genes that have been reverse transcribed from mRNA and inserted back into the genome. They often lack introns and regulatory sequences, and their expression depends on nearby promoters.

Mechanism of Retrotransposition

The process of retrotransposition involves several key steps:

1. Transcription: The retroelement is transcribed into RNA by the host cell's RNA polymerase. 2. Reverse Transcription: The RNA is reverse transcribed into complementary DNA (cDNA) by reverse transcriptase. 3. Integration: The cDNA is integrated into a new location in the genome by integrase or other recombination mechanisms.

Impact on Genomes

Retroelements play a crucial role in shaping the structure and function of genomes. They can:

• Drive Evolution: By creating genetic diversity and new gene combinations.
• Regulate Gene Expression: Through insertional mutagenesis and the provision of alternative promoters.
• Cause Genetic Disorders: When insertions disrupt functional genes or regulatory regions.

Research and Applications

Retroelements are studied for their role in:

• Evolutionary Biology: Understanding the evolutionary history and relationships between species.
• Genetic Engineering: Utilizing retroviral vectors for gene therapy.
• Disease Research: Investigating their role in cancer and other diseases.

Also see

• Transposon
• Reverse Transcriptase
• Endogenous Retrovirus
• Gene Therapy