RNase PH

{{Short description|Type of enzyme}}

{{protein

| Name = Ribonuclease PH

| caption = Structure of the RNase PH hexamer

| image = Crystal structure 1UDN.jpg

| width = 220

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| Symbol = RNASEPH

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| ECnumber = 2.7.7.56

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RNase PH is a tRNA nucleotidyltransferase, present in archaea and bacteria, that is involved in tRNA processing. Contrary to hydrolytic enzymes, it is a phosphorolytic enzyme, meaning that it uses inorganic phosphate as a reactant to cleave nucleotide-nucleotide bonds, releasing diphosphate nucleotides. The active structure of the proteins is a homohexameric complex, consisting of three ribonuclease (RNase) PH dimers.{{cite journal | vauthors = Ishii R, Nureki O, Yokoyama S | title = Crystal structure of the tRNA processing enzyme RNase PH from Aquifex aeolicus | journal = The Journal of Biological Chemistry | volume = 278 | issue = 34 | pages = 32397–404 | date = August 2003 | pmid = 12746447 | doi = 10.1074/jbc.M300639200 | doi-access = free }} RNase PH has homologues in many other organisms, which are referred to as RNase PH-like proteins. The part of another larger protein with a domain that is very similar to RNase PH is called an RNase PH domain (RPD).