Piwi
Piwi domain | |||||||||||
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Identifiers | |||||||||||
Symbol | Piwi | ||||||||||
Pfam | PF02171 | ||||||||||
InterPro | IPR003165 | ||||||||||
PROSITE | PS50822 | ||||||||||
CDD | cd02826 | ||||||||||
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Piwi (or PIWI)
Protein structure and function
The structure of several Piwi and Argonaute proteins (Ago) have been solved. Piwi proteins are RNA-binding proteins with 2 or 3 domains: The N-terminal PAZ domain binds the 3'-end of the guide RNA; the middle MID domain binds the 5'-phosphate of RNA; and the C-terminal PIWI domain acts as an RNase H endonuclease that can cleave RNA.[9][10] The small RNA partners of Ago proteins are microRNAs (miRNAs). Ago proteins utilize miRNAs to silence genes post-transcriptionally or use small-interfering RNAs (siRNAs) in both transcription and post-transcription silencing mechanisms. Piwi proteins interact with piRNAs (28–33 nucleotides) that are longer than miRNAs and siRNAs (~20 nucleotides), suggesting that their functions are distinct from those of Ago proteins.[9]
Human Piwi proteins
Presently there are four known human Piwi proteins—PIWI-like protein 1, PIWI-like protein 2, PIWI-like protein 3 and PIWI-like protein 4. Human Piwi proteins all contain two RNA binding domains, PAZ and Piwi. The four PIWI-like proteins have a spacious binding site within the PAZ domain which allows them to bind the bulky 2’-OCH3 at the 3’ end of piwi-interacting RNA.[11]
One of the major human
Homologous proteins in mice have been called miwi (for mouse piwi).[13]
Role in germline cells
PIWI proteins play a crucial role in fertility and germline development across animals and ciliates. Recently identified as a polar granule component, PIWI proteins appear to control germ cell formation so much so that in the absence of PIWI proteins there is a significant decrease in germ cell formation. Similar observations were made with the mouse homologs of PIWI, MILI, MIWI and MIWI2. These homologs are known to be present in spermatogenesis. Miwi is expressed in various stages of spermatocyte formation and spermatid elongation where Miwi2 is expressed in
Role in RNA interference
The piwi domain
Recent evidence suggests that the functional role of piwi proteins in germ-line determination is due to their capacity to interact with miRNAs. Components of the miRNA pathway appear to be present in pole plasm and to play a key role in early development and morphogenesis of Drosophila melanogaster embryos, in which germ-line maintenance has been extensively studied.[18]
piRNAs and transposon silencing
A novel class of longer-than-average miRNAs known as
Although their biogenesis is not yet well understood, piRNAs and Piwi proteins are thought to form an endogenous system for silencing the expression of
Footnotes
References
- ^ S2CID 2021813.
- PMID 27899622.
- ^ Lindse K (2013). "Piwi-RNAs, the Defenders of the Genome".
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(help) - PMID 10631171.
- PMID 24429634.
- PMID 9199372.
- PMID 9851978.
- PMID 23297219.
- ^ PMID 21465557.
- S2CID 25990631.
- PMID 21193640.
- PMID 12037681.
- PMID 12062093.
- PMID 23712694.
- PMID 19575643.
- PMID 11050429.
- PMID 15800629.
- S2CID 6397874.
- PMID 16882976.
- S2CID 3185036.
- ^ S2CID 40471466.
- PMID 16882972.
- S2CID 53565676.
External links
- SCOP
- PDOC50822 – Piwi domain in PROSITE
- UNIPROT Piwi - Piwi domains