This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Degradation/Utilization/Assimilation → Nucleosides and Nucleotides Degradation → Purine Nucleotides Degradation|
A bewildering number of post-transcriptional modifications are introduced into cellular RNAs by different enzymes [FerreDAmare03]. The most abundant post-transcriptional nucleobase modification in cellular RNAs is the isomerization of uridine to pseudouridine, which is carried out by the enzyme pseudouridine synthase in a reaction that does not require any cofactors. In pseudouridine uracil is bound to the to ribose through C5 rather than through N1 as is the case for uridine. The synthase severs the normal glycosidic C-N bond of uridine, flips the uracil moiety along its N3-C6 axis, and forms a glycosidic C-C bond with C5. Pseudouridine is one of few molecules that have a glycosidic C-C bond.
Pseudouridine synthases belong to four different families, which are represented in Escherichia coli by the truA, truB, rluA and rsuA. The only sequence element that is absolutely conserved among the four families of enzymes is a catalytic aspartic acid [Huang98, Del01, Ramamurthy99].
Pseudouridylation is found in organisms from all kingdoms. Mammalian rRNA contains about 100 pseudouridines per ribosome, and tRNAs contain an average of 3 - 4 pseudouridines. While many eukaryotes possess the ability to degrade pseudouridine, mammals appear to have lost this ability, and pseudouridine is excreted in their urine.
Pseudouridine has been shown to serve as a source of uracil for a strain of Escherichia coli that is deficient in pyrimidine synthesis [Breitman68]. It was shown that pseudouridine was first phosphorylated by a kinase to pseudouridine 5'-phosphate [Solomon71], followed by hydrolysis to D-ribose 5-phosphate and uracil [Breitman70]. The genes encoding these two enzymes have been discovered in Escherichia coli UTI89, a uropathogenic strain [Preumont08]. The genes were cloned, and the enzymes were purified and characterized, conforming the proposed function.
Similar genes were found in the genomes of many bacteria and almost all eukaryotes [Preumont08].
Variants: purine deoxyribonucleosides degradation I, purine deoxyribonucleosides degradation II, purine nucleobases degradation I (anaerobic), purine nucleobases degradation II (anaerobic), purine nucleotides degradation I (plants), purine nucleotides degradation II (aerobic), purine ribonucleosides degradation, urate biosynthesis/inosine 5'-phosphate degradation
Unification Links: EcoCyc:PWY-6019
Huang98: Huang L, Pookanjanatavip M, Gu X, Santi DV (1998). "A conserved aspartate of tRNA pseudouridine synthase is essential for activity and a probable nucleophilic catalyst." Biochemistry 37(1);344-51. PMID: 9425056
Snyder04: Snyder JA, Haugen BJ, Buckles EL, Lockatell CV, Johnson DE, Donnenberg MS, Welch RA, Mobley HL (2004). "Transcriptome of uropathogenic Escherichia coli during urinary tract infection." Infect Immun 72(11);6373-81. PMID: 15501767
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