Phylogenetic tree of marsupials derived from retroposon data - journal

Retroposons are repetitive DNA fragments which are inserted into

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins ar ...

s after they had been reverse transcribed from any RNA molecule.

Difference between retroposons and retrotransposons

In contrast to

retrotransposon Retrotransposons (also called Class I transposable elements or transposons via RNA intermediates) are a type of genetic component that copy and paste themselves into different genomic locations ( transposon) by converting RNA back into DNA throu ...

s, retroposons never encode

reverse transcriptase A reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template, a process termed reverse transcription. Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genom ...

(RT) (but see below). Therefore, they are non-autonomous elements with regard to transposition activity (as opposed to

transposon A transposable element (TE, transposon, or jumping gene) is a nucleic acid sequence in DNA that can change its position within a genome, sometimes creating or reversing mutations and altering the cell's genetic identity and genome size. Tra ...

s). Non-long terminal repeat (LTR) retrotransposons such as the human LINE1 elements are sometimes falsely referred to as retroposons. However, this depends on the author. For example,

Howard Temin Howard Martin Temin (December 10, 1934 – February 9, 1994) was an American geneticist and virologist. He discovered reverse transcriptase in the 1970s at the University of Wisconsin–Madison, for which he shared the 1975 Nobel Prize in Phy ...

published the following definition: Retroposons encode RT but are devoid of long terminal repeats (LTRs), for example long interspersed elements (LINEs). Retrotransposons also feature LTRs and

retroviruses A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. Once inside the host cell's cytoplasm, the virus uses its own reverse transcriptas ...

, in addition, are packaged as viral particles (virions). Retrosequences are non-autonomous elements devoid of RT. They are retroposed with the aid of the machinery of autonomous elements, such as LINEs; examples are

short interspersed nuclear element Short interspersed nuclear elements (SINEs) are non-autonomous, non-coding transposable elements (TEs) that are about 100 to 700 base pairs in length. They are a class of retrotransposons, DNA elements that amplify themselves throughout eukaryot ...

s (SINEs) or mRNA-derived retro(pseudo)genes.

Gene duplications

Retroposition accounts for approximately 10,000 gene-duplication events in the human genome, of which approximately 2-10% are likely to be functional. Such genes are called retrogenes and represent a certain type of retroposon. A classical event is the retroposition of a spliced pre-mRNA molecule of the c-src gene into the proviral ancestor of the Rous Sarcoma Virus (RSV). The retroposed c-src pre-mRNA still contained a single

intron An intron is any Nucleic acid sequence, nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''intragenic region'', i.e. a region inside a gene."The notion of ...

and within RSV is now referred to as v-src gene.

References

Mobile genetic elements Molecular biology {{genetics-stub