{PDOC50822}
{PS50822; PIWI}
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* Piwi domain profile *
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The Piwi  box  (or  Sting  domain)  is  an about 40 to 80 amino-acid conserved
region, which  was  first identified in the C-terminal part of Drosophila Piwi
and Sting  proteins,  and  of  related  proteins  from  human,  Caenorhabditis
elegans, Arabidopsis  thaliana, fission yeast and Dictyostelium discoideum [1,
2]. It  was  later  recognized  that this conserved region is part of a larger
300-amino-acid domain,  called  Piwi,  which is also found in some prokaryotic
proteins of  unknown  function  [3].  The  Piwi domain containing proteins are
often involved  in  stem-cell  maintenance  and/or  post-transcriptional  gene
silencing (PTGS)  through RNA interference (RNAi), the mechanism through which
double-stranded RNAs (dsRNAs) silence cognate genes [3]. Neither the structure
nor the function of the Piwi domain are known.

Some proteins known to contain a Piwi domain are listed below:

 - Drosophila  Piwi protein. It is a nuclear protein that acts a key regulator
   of stem  cell  division.  Its  somatic  expression  modulates the number of
   germline stem  cells  and  the  rate  of their division, while its germline
   expression also  contributes  to  promoting  stem  cell division in a cell-
   autonomous manner. The Piwi domain is essential for its function [4].
 - Drosophila  Sting  protein. It could repress general or specific transcript
   processing.
 - Human Hiwi (for human Piwi) protein. It might play a role in maintenance of
   stem cell  quiescence  or  downregulation  of  stem cell or progenitor cell
   cycling.
 - Caenorhabditis  elegans  Piwi-related  proteins  1 and 2 (prg-1 and prg-2).
   They are also required for germ-line self-renewal.
 - Caenorhabditis elegans RNA Interference Deficient 1 (rde-1). It is required
   for RNAi and transposon silencing.
 - Arabidopsis  thaliana  Argonaute  (Ago)  protein. It is involved in RNAi as
   well as  in  leaves  and  floral  organs development and axillary meristems
   formation.
 - Arabidopsis  thaliana  Zwille (Zll) or Pinhead (Pnh). It is a developmental
   protein required  for  reliable  formation  of  primary  and axillary shoot
   apical meristems.
 - Eukaryotic  translation initiation factor 2C (eIF2C). It plays an important
   role in the eukaryotic peptide chain initiation process.

The profile we have developed covers the entire Piwi domain.

-Sequences known to belong to this class detected by the profile: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.
-Last update: May 2002 / First entry.

[ 1] Cox D.N., Chao A., Baker J., Chang L., Qiao D., Lin H.
     "A novel class of evolutionarily conserved genes defined by piwi are
     essential for stem cell self-renewal."
     Genes Dev. 12:3715-3727(1998).
     PubMed=9851978
[ 2] Schmidt A., Palumbo G., Bozzetti M.P., Tritto P., Pimpinelli S.,
     Schafer U.
     "Genetic and molecular characterization of sting, a gene involved in
     crystal formation and meiotic drive in the male germ line of
     Drosophila melanogaster."
     Genetics 151:749-760(1999).
     PubMed=9927466
[ 3] Cerutti L., Mian N., Bateman A.
     "Domains in gene silencing and cell differentiation proteins: the
     novel PAZ domain and redefinition of the Piwi domain."
     Trends Biochem. Sci. 25:481-482(2000).
     PubMed=11050429
[ 4] Cox D.N., Chao A., Lin H.
     "piwi encodes a nucleoplasmic factor whose activity modulates the
     number and division rate of germline stem cells."
     Development 127:503-514(2000).
     PubMed=10631171

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