P-bodies
The processing bodies ( P-bodies, in mammals, GW bodies, mammalian P-bodies, Dcp -containing bodies or mRNA decay foci called ) are microscopic, bounded structures (aggregates ) in the eukaryotic cell, consisting of enzymes, the mRNA in degradation play an important role.
History
P-bodies have been described in S. cerevisiae 2003. As early as 1997 reported Bashkirov and employees that the main 5' -3 ' exonuclease ( "discrete, prominent foci " ) from eukaryotic cells, Xrn1p, in separate, distinctive centers vorliege enriched.
Composition
The exact composition of P-bodies is still under discussion. It also differs in different organisms. P-bodies consist mainly of complexes of mRNA and protein of the 5'-3 ' of mRNA degradation. The latter include enzymes to remove the 5'- cap structure of mRNA and a 5'-3 ' exonuclease ( Xrn1p ).
Formation
Thus, P-bodies arise, the poly ( A) tail of mRNA must first be deadenyliert; Here, the number of attached adenine nucleotides significantly reduced. This is usually also the beginning of the 5'- 3 'or 3'-5' mRNA degradation. Then, the enzymes of the 5'-3 ' mRNA degradation assemble the apparatus (see above) to that mRNA, forming a mRNP. However, the mechanism, such as individual aggregate mRNPs to P-bodies, still unknown. P-bodies may have different sizes.
Functions
As will be noted in P-bodies mRNAs, they can be removed from the translation machinery. These interact mRNAs from polysomes at defects of the translation initiation or -termination with enzymes of mRNA decay and form P-bodies. From there, the mRNAs can then either return to the Translationsmachinerie, such as when yeasts grow again after a stationary phase or a specific stress stimulus is no longer present.
Alternatively, the mRNAs in P-bodies can be finally removed.
P-bodies enable the cell to separate the mRNA degradation machinery of active sites of the translation. This could counteract an inappropriate or premature degradation of mRNAs. In addition, P-bodies form a kind of buffer. An excessive amount of mRNAs would strongly compete for translation factors, so that the translation as a whole would not proceed effectively. Finally, the temporary retention of mRNAs in P-bodies can handle problems with defective translation complexes. This could also be viewed as a kind of chaperone function for mRNAs: mRNAs are left like polypeptides in a functionally competent state.