Alu sequence

Overview

An Alu sequence is a short stretch of DNA originally characterized by the action of the restriction endonuclease AluI. Alu sequences are a type of Short Interspersed Nuclear Element (SINE) and are the most abundant transposable elements in the human genome. They are approximately 300 base pairs in length and are found in over one million copies, making up about 10% of the human genome.

Structure

Alu sequences are typically around 300 base pairs long and are composed of two similar but distinct monomers joined by an A-rich linker region. Each monomer contains a RNA polymerase III promoter, which is essential for the transcription of the Alu element. The 3' end of the Alu sequence is characterized by a poly-A tail, which is a hallmark of retrotransposons.

Function

Alu sequences do not encode proteins but can influence gene expression and genome evolution. They can insert themselves into new genomic locations, potentially disrupting genes or regulatory regions. Alu elements can also contribute to genomic recombination and genetic diversity.

Mechanism of Transposition

Alu sequences transpose through a "copy and paste" mechanism known as retrotransposition. This process involves the transcription of the Alu element into RNA, followed by reverse transcription into DNA, which is then inserted into a new location in the genome. The enzyme reverse transcriptase, often provided by Long Interspersed Nuclear Elements (LINEs), is crucial for this process.

Impact on Human Health

Alu insertions can have significant effects on human health. They can cause genetic disorders if they insert into or near essential genes. Alu insertions have been associated with diseases such as hemophilia, cystic fibrosis, and certain types of cancer. However, they can also contribute to beneficial genetic variation and adaptation.

Evolutionary Significance

Alu sequences are thought to have originated from the 7SL RNA gene, a component of the signal recognition particle. They have proliferated extensively in primate genomes, particularly in humans. The high copy number and widespread distribution of Alu elements make them useful markers for studying human evolution and population genetics.

Research Applications

Alu sequences are used in various research applications, including phylogenetic studies, forensic analysis, and the study of genomic instability. Their presence in the genome can be used to trace lineage and evolutionary relationships among primates.

See Also

• Transposable element
• Retrotransposon
• Genomic variation
• Human genome

External Links

• [Human Genome Project]
• [Ensembl Genome Browser]

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