Question

What is the purpose of an alu repetetive sequence?

Answer 1

Alu repetitive sequences are SINE transposable elements of around 300 bp that can move along the genome. RNA polymerase transcribes Alu sequences, which can then be converted to ds DNA by reverse transcriptase. They require L1 transposon for transposition.

They regulate tissue specific expression of genes. As they can insert themselves in any position of genome, they can activate or repress transcription of genes due to gene activation or gene silencing. They can form new combination of genes or even duplicate genes. This has relevance in evolution. Although, they have been considered as junk DNA in human genome, it is now increasingly been understood that they may have biological function as yet which are not deciphered. They have been observed in introns of coding genes. If these intronic Alu sequences obtain introns, then normal gene function can be affected. Intronic Alu in CD8α gene in humans has binding sites for includes transcription factors. They can be involved in chromosomal rearrangements via homologous recombination, insertion and deletions. Differences exist in DNA methylation patterns in Alu sequences in germ cells of female and males. Thus, they may have a role in genomic imprinting. Alu sequences are substrates for activity of RNA pol III in the transcripts formed by RNA pol III.