RNase R, or Ribonuclease R, is a 3'-->5'
exoribonuclease, which belongs to the
RNase II Ribonuclease II may refer to one of two enzymes:
* Ribonuclease T2
*Exoribonuclease II
Exoribonuclease II (, ''ribonuclease II'', ''ribonuclease Q'', ''BN ribonuclease'', ''Escherichia coli exo-RNase II'', ''RNase II'', ''exoribonuclease (misleadin ...
superfamily, a group of enzymes that hydrolyze RNA in the 3' - 5' direction. RNase R has been shown to be involved in selective
mRNA degradation, particularly of non stop mRNAs in bacteria. RNase R has
homologues in many other organisms.
When a part of another larger protein has a
domain
Domain may refer to:
Mathematics
*Domain of a function, the set of input values for which the (total) function is defined
**Domain of definition of a partial function
**Natural domain of a partial function
**Domain of holomorphy of a function
* Do ...
that is very similar to RNase R, this is called an RNase R domain.
Role in ''trans''-translation and ribosomal quality control
RNase R ensures translation accuracy, correct
rRNA maturation and elimination of abnormal rRNAs, and is employed by the ''trans''-translation system to break down damaged mRNAs.
In ''
Escherichia coli,'' RNase R is a 92 kD protein, with the characteristic capacity to degrade structured RNA substrates without displaying sequence specificity. Therefore, RNase R acts over a range of substrates, such as, ribosomal, transfer, messenger and small non-coding RNAs. RNase R is associated with ribonucleoprotein complex that contains tmRNA and SmpB, and is involved in the development of tmRNA under cold-shock.
RNase R is also associated with
ribosome
Ribosomes ( ) are macromolecular machines, found within all cells, that perform biological protein synthesis (mRNA translation). Ribosomes link amino acids together in the order specified by the codons of messenger RNA (mRNA) molecules to ...
s and participates in
rRNA, or ribosomal RNA, quality control processes. RNase R has an ''
in vitro'' affinity for rRNA. In several rRNA quality control pathways, RNase R behaves as a mainfactor by enhancing the removal of faulty rRNA molecules. This protein is also critical for handling rRNA precursors and for observing the ribosome integrity.
RNA digestion
RNase R has two cold shock domains, an RNase catalytic domain, an S1 domain and a basic domain.
Overabundance of RNase R in a cell are harmful since RNase R is more active and more effective in breaking down RNAs than the other bacterial exoribonucleases, such as
RNase II Ribonuclease II may refer to one of two enzymes:
* Ribonuclease T2
*Exoribonuclease II
Exoribonuclease II (, ''ribonuclease II'', ''ribonuclease Q'', ''BN ribonuclease'', ''Escherichia coli exo-RNase II'', ''RNase II'', ''exoribonuclease (misleadin ...
. Besides the substrate RNAs that construct double-stranded RNA with 3' overhangs shorter than seven nucleotides, RNase R can degrade all linear RNAs.
For the methodical digestion of eukaryotic linear RNAs, RNase R is a good 3' to 5' exoribonuclease but there are infrequent cases of RNase R resistance. Since mRNAs are not chemically protected at their 3' ends, unlike the protection provided at their 5' ends by the cap structure, RNase R successfully degrades linear mRNAs from their unprotected 3' ends.
References
Ribonucleases
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