P-body

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The processing bodies ( P-bodies , in mammals also GW bodies , mammalian P-bodies , Dcp-containing bodies or mRNA-decay foci ) are microscopic, demarcated structures (aggregates) in the eukaryotic cell , consisting of enzymes contained in the mRNA -Degradation play an important role.

History

P bodies were described in S. cerevisiae in 2003 . As early as 1997, Bashkirov and co-workers reported that the most important 5'– 3 ' exonuclease from eukaryotic cells, Xrn1p, was present in accumulated separate, prominent centers (“ discrete, prominent foci ”).

composition

The exact composition of P-bodies is still being discussed. It also differs in different organisms. P-bodies mainly consist of complexes of mRNAs and proteins of the 5'-3 'mRNA breakdown. The latter include enzymes that remove the 5'-cap structure of mRNAs and a 5'-3 ' exonuclease (Xrn1p).

Emergence

In order for P bodies to arise, the poly (A) tail of mRNA must first be deadenylated; this reduces the number of attached adenine nucleotides considerably. This is usually also the beginning of the 5'-3 'or 3'-5' mRNA degradation. Then the enzymes of the 5'-3 'mRNA degradation apparatus (see above) assemble on this mRNA and form an mRNP . However, the mechanism by which individual mRNPs aggregate to form P bodies is still unknown. P-bodies can have different sizes.

Functions

Since mRNAs are retained in P-bodies, they can be withdrawn from the translation machinery. In the case of defects in translation initiation or termination, mRNAs from polysomes interact with enzymes involved in mRNA degradation and form P bodies. From there, the mRNAs can either get back into the translation machinery, for example when yeasts grow again after a stationary phase or a particular stress stimulus is no longer present.

Alternatively, the mRNAs can finally also be broken down in P-bodies.

P-bodies enable the cell to separate the mRNA degradation machinery from active sites of translation. This could counteract an unsuitable or premature degradation of mRNAs. In addition, P-bodies form a kind of buffer. Too high a quantity of mRNAs would compete too strongly for translation factors, so that the translation would not take place effectively overall. Finally, the temporary retention of the mRNAs in P-bodies can avoid problems with defective translation complexes. This could also be seen as a kind of chaperone function for mRNAs: like polypeptides, mRNAs are left in a functionally competent state.

credentials

  1. ↑ Bashkirov, VI. et al . (1997): A mouse cytoplasmic exoribonuclease (mXRN1p) with preference for G4 tetraplex substrates. In: J Cell Biol . 136 (4); 761-773; PMID 9049243 , PMC 2132493 (free full text)
  2. ↑ Eulalio, A. et al . (2007): P bodies: at the crossroads of post-transcriptional pathways. In: Nat Rev Mol Cell Biol 8 (1); 9-22; PMID 17183357 ; doi : 10.1038 / nrm2080
  3. ↑ Brengues, M. et al . (2005): Movement of eukaryotic mRNAs between polysomes and cytoplasmic processing bodies . In: Science 310 (5747); 486-489; PMID 16141371
  4. ↑ Bhattacharyya, SN. et al. (2006): Relief of microRNA-mediated translational repression in human cells subjected to stress. In: Cell 125 (6); 1111-1124; PMID 16777601

literature

  • Marx, J. (2005): Molecular biology. P-bodies mark the spot for controlling protein production . In: Science 310 (5749); 764-765; PMID 16272094
  • Parker, R. and Sheth, U. (2007): P bodies and the control of mRNA translation and degradation . In: Mol Cell . 25 (5); 635-646; PMID 17349952