Editing Alu element (section)

==Alu elements==

Some ''Alu'' elements are responsible for regulation of tissue-specific genes. Others are involved in the transcription of nearby genes and can sometimes change the way a gene is expressed.<ref name=pmid8790336>{{cite journal |pmid=8790336 |pmc=38434 |year=1996 |last1=Britten |first1=R. J |title=DNA sequence insertion and evolutionary variation in gene regulation |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=93 |issue=18 |pages=9374–7 |doi=10.1073/pnas.93.18.9374|bibcode=1996PNAS...93.9374B |doi-access=free }}</ref>

''Alu'' elements are [[retrotransposon]]s and look like DNA copies made from [[RNA polymerase III]]-encoded RNAs. ''Alu'' elements do not encode for protein products. They are replicated as any other DNA sequence, but depend on [[Long interspersed nuclear element|LINE]] retrotransposons for generation of new elements, thus providing an easy explanation for their presence in large numbers in primate genomes.<ref name=pmid16344113>{{cite journal |doi=10.1016/S0074-7696(05)47004-7 |pmid=16344113 |title=Short Retroposons in Eukaryotic Genomes |journal=International Review of Cytology |volume=247 |pages=165–221 |year=2005 |last1=Kramerov |first1=D |last2=Vassetzky |first2=N }}</ref>

''Alu'' element replication and mobilization begins by interactions with [[signal recognition particle]]s (SRPs), which aid newly translated proteins to reach their final destinations.<ref name=pmid11089964>{{cite journal |doi=10.1038/35041507 |pmid=11089964 |title=Structure and assembly of the Alu domain of the mammalian signal recognition particle |journal=Nature |volume=408 |issue=6809 |pages=167–73 |year=2000 |last1=Weichenrieder |first1=Oliver |last2=Wild |first2=Klemens |last3=Strub |first3=Katharina |last4=Cusack |first4=Stephen |bibcode=2000Natur.408..167W |s2cid=4427070 |url=http://archive-ouverte.unige.ch/unige:17516 }}</ref> ''Alu'' RNA forms a specific RNA:protein complex with a protein heterodimer consisting of SRP9 and SRP14.<ref name="pmid11089964"/> SRP9/14 facilitates ''Alu''<nowiki/>'s attachment to ribosomes that capture nascent [[LINE1|L1 proteins]]. Thus, an ''Alu'' element can take control of the L1 protein's [[reverse transcriptase]], ensuring that the ''Alu''<nowiki/>'s RNA sequence gets copied into the genome rather than the L1's mRNA.<ref name="pmid18836035"/>

''Alu'' elements in primates form a fossil record that is relatively easy to decipher because ''Alu'' element insertion events have a characteristic signature that is both easy to read and faithfully recorded in the genome from generation to generation. The study of ''Alu Y'' elements (the more recently evolved) thus reveals details of ancestry because individuals will most likely only share a particular ''Alu'' element insertion if they have a common ancestor. This is because insertion of an Alu element occurs only 100 - 200 times per million years, and no known mechanism for the targeted deletion of one has been found. Therefore, individuals with an element likely descended from an ancestor with one—and vice versa, for those without. In genetics, the presence or lack thereof of a recently inserted ''Alu'' element may be a good property to consider when studying human evolution.<ref>{{Cite journal|last1=Terreros|first1=Maria C.|last2=Alfonso-Sanchez|first2=Miguel A.|last3=Novick|last4=Luis|last5=Lacau|last6=Lowery|last7=Regueiro|last8=Herrera|date=September 11, 2009|title=Insights on human evolution: an analysis of Alu insertion polymorphisms|journal=Journal of Human Genetics|volume=54|issue=10|pages=603–611|doi=10.1038/jhg.2009.86|pmid=19745832|s2cid=8153502|doi-access=free}}</ref> Most human ''Alu'' element insertions can be found in the corresponding positions in the genomes of other primates, but about 7,000 ''Alu'' insertions are unique to humans.<ref name=pmid16136131>{{cite journal |doi=10.1038/nature04072 |pmid=16136131 |title=Initial sequence of the chimpanzee genome and comparison with the human genome |journal=Nature |volume=437 |issue=7055 |pages=69–87 |year=2005 |bibcode=2005Natur.437...69. |author1=Chimpanzee Sequencing Analysis Consortium |s2cid=2638825 |doi-access=free }}</ref>