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Target Concepts:
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Query: EC:3.1.27.5 (
RNase
)
17,967
document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)
The substrate specificity of the ubiquitin (Ub) conjugation system was explored with regard to recognition of unfolded conformation and/or oxidized methionine residues in six derivatives of bovine
RNase A
. Based on the following observations, ubiquitination of
RNase A
substrates by the enzymes in a rabbit reticulocyte extract appears to correlate with unfolded conformation rather than with methionine oxidation. 1) Methionine oxidation in already unfolded forms of
RNase A
does not enhance ubiquitination. 2) Fluorescence measurements and iodoacetate trapping of free sulfhydryls show that the disulfide bonds of MetSO-
RNase A
, in which the 4 methionine residues are oxidized to the sulfoxide, are reduced by 2 mM dithiothreitol (DTT) in standard Ub conjugation assays so that this derivative also is unfolded. 3) Although MetSO-
RNase A
is ubiquitinated in the absence of DTT, its intrinsic fluorescence, cation-exchange properties, and susceptibility to reduction indicate a non-native conformation. 4)
Methionine sulfoxide
-containing peptides that mimic regions of
RNase A
fail to inhibit conjugation of 125I-Ub to MetSO-
RNase A
. Ub adducts to two of the six derivatives (MetSO- and reduced/carboxamidomethylated MetSO-
RNase A
) increase when DTT is omitted from the reactions. Ubaldehyde, an inhibitor of isopeptidases that disassemble Ub-protein conjugates, increased product yields and reduced or abolished the DTT effect, suggesting that an isopeptidase specific for these two
RNase A
derivatives may be inactivated by oxidation. Ub conjugates of the other
RNase A
derivatives also increase with Ub-aldehyde but are unaffected by DTT.
...
PMID:Recognition of modified forms of ribonuclease A by the ubiquitin system. 255 Apr 56
Controlling iron homeostasis is crucial for all aerobically grown living cells that are exposed to oxidative damage by reactive oxygen species (ROS), as free iron increases the production of ROS.
Methionine sulfoxide
reductases (Msr) are key enzymes in repairing ROS-mediated damage to proteins, as they reduce oxidized methionine (MetSO) residues to methionine. E. coli synthesizes two Msr, A and B, which exhibit substrate diastereospecificity. The bacterial iron-responsive small RNA (sRNA) RyhB controls iron metabolism by modulating intracellular iron usage. We show in this paper that RyhB is a direct regulator of the msrB gene that encodes the MsrB enzyme. RyhB down-regulates msrB transcripts along with Hfq and RNaseE proteins since mutations in the ryhB, fur, hfq, or RNaseE-encoded genes resulted in iron-insensitive expression of msrB. Our results show that RyhB binds to two sequences within the short 5'UTR of msrB mRNA as identified by reverse transcriptase and
RNase
and lead (II) protection assays. Toeprinting analysis shows that RyhB pairing to msrB mRNA prevents efficient ribosome binding and thereby inhibits translation initiation. In vivo site directed-mutagenesis experiments in the msrB 5'UTR region indicate that both RyhB-pairing sites are required to decrease msrB expression. Thus, this study suggests a novel mechanism of translational regulation where a same sRNA can basepair to two different locations within the same mRNA species. In contrast, expression of msrA is not influenced by changes in iron levels.
...
PMID:The sRNA RyhB regulates the synthesis of the Escherichia coli methionine sulfoxide reductase MsrB but not MsrA. 2367 89
