Pseudouridine (5-ribosyluracil, abbreviated by the Greek letter psi- Ψ)[1] is an isomer of the nucleosideuridine in which the uracil is attached via a carbon-carbon instead of a nitrogen-carbon glycosidic bond.
Pseudouridine is the most abundant RNA modification in cellular RNA[2] and one of over 100 chemically distinct modifications that may affect translation or other functions of RNA. Pseudouridine is the C5-glycoside isomer of uridine that contains a C-C bond between C1 of the ribose sugar and C5 of uracil, rather than usual C1-N1 bond found in uridine. Uridine is converted to pseudouridine by rotating the uridine molecule 180° across its N3-C6 axis.[3] The C-C bond gives it more rotational freedom and conformational flexibility.[4] In addition, pseudouridine has an extra hydrogen bond donor at the N1 position.
Pseudouridine is a ubiquitous constituent of structural RNA (transfer, ribosomal, small nuclear (snRNA) and small nucleolar), and present in mRNA, across the three phylogenetic domains of life and was the first discovered. It accounts for 4% of the nucleotides in yeasttRNA.[5] This base modification is able to stabilize RNA and improve base-stacking by forming additional hydrogen bonds with water through its extra imino group.[6] There are 11 pseudouridines in Escherichia coli rRNA, 30 in yeast cytoplasmic rRNA and a single modification in mitochondrial 21S rRNA and about 100 pseudouridines in human rRNA indicating that the extent of pseudouridylation increases with the complexity of an organism.[7] Pseudouridine was also detected in the Leishmania donovani genome. 18 pseudouridine modification sites were detected in the peptidyl transferase entry site and in the mRNA entry tunnel in protein translation. These modifications in the parasite lead to increased protein synthesis and growth rate.[8]
Pseudouridine in rRNA and tRNA has been shown to fine-tune and stabilize the regional structure and help maintain their functions in mRNA decoding, ribosome assembly, processing and translation.[4][9][10] Pseudouridine in snRNA has been shown to enhance spliceosomal RNA-pre-mRNA interaction to facilitate splicing regulation.[11]