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RNase PH-like 3'-5' exoribonucleases RNase PH-like 3'-5' exoribonucleases are enzymes that catalyze the 3' to 5' processing and decay of RNA substrates. Evolutionarily related members can be fond in prokaryotes, archaea, and eukaryotes. Bacterial ribonuclease PH contains a single copy of this domain, and removes nucleotide residues following the -CCA terminus of tRNA. Polyribonucleotide nucleotidyltransferase (PNPase) contains two tandem copies of the domain and is involved in mRNA degradation in a 3'-5' direction. Archaeal exosomes contain two individually encoded RNase PH-like 3'-5' exoribonucleases and are required for 3' processing of the 5.8S rRNA. The eukaryotic exosome core is composed of six individually encoded RNase PH-like subunits, but it is not a phosphorolytic enzyme per se; it directly associates with Rrp44 and Rrp6, which are hydrolytic exoribonucleases related to bacterial RNase II/R and RNase D. All members of the RNase PH-like family form ring structures by oligomerization of six domains or subunits, except for a total of 3 subunits with tandem repeats in the case of PNPase, with a central channel through which the RNA substrate must pass to gain access to the phosphorolytic active sites. |
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Jiyao W et al.(2023). "The conserved domain database in 2023.",