EC Explorer

6.5.1.8

3′-phosphate/5′-hydroxy nucleic acid ligase

(1) (ribonucleotide)_n-3′-phosphate + 5′-hydroxy-(ribonucleotide)_m + GTP = (ribonucleotide)_n+m + GMP + diphosphate (overall reaction);;(1a) GTP + [RNA ligase]-L-histidine = [RNA ligase]-N^τ-(5′-guanosyl-phosphono)-L-histidine + diphosphate;;(1b) [RNA ligase]-N^τ-(5′-guanosyl-phosphono)-L-histidine + (ribonucleotide)_n-3′-phosphate = (ribonucleotide)_n-3′-(5′-diphosphoguanosine) + [RNA ligase]-L-histidine;;(1c) (ribonucleotide)_n-3′-(5′-diphosphoguanosine) + 5′-hydroxy-(ribonucleotide)_m = (ribonucleotide)_n+m + GMP;;(2) (ribonucleotide)_n-2′,3′-cyclophosphate + 5′-hydroxy-(ribonucleotide)_m + GTP + H₂O = (ribonucleotide)_n+m + GMP + diphosphate (overall reaction);;(2a) (ribonucleotide)_n-2′,3′-cyclophosphate + H₂O = (ribonucleotide)_n-3′-phosphate;;(2b) GTP + [RNA ligase]-L-histidine = [RNA ligase]-N^τ-(5′-guanosyl-phosphono)-L-histidine + diphosphate;;(2c) [RNA ligase]-N^τ-(5′-guanosyl-phosphono)-L-histidine + (ribonucleotide)_n-3′-phosphate = (ribonucleotide)_n-3′-(5′-diphosphoguanosine) + [RNA ligase]-L-histidine;;(2d) (ribonucleotide)_n-3′-(5′-diphosphoguanosine) + 5′-hydroxy-(ribonucleotide)_m = (ribonucleotide)_n+m + GMP

rtcB (gene name)

poly(ribonucleotide)-3′-phosphate:5′-hydroxy-poly(ribonucleotide) ligase (GMP-forming)

The enzyme is a GTP- and Mn²⁺-dependent 3′-5′ nucleic acid ligase with the ability to join RNA with 3′-phosphate or 2′,3′-cyclic-phosphate ends to RNA with 5′-hydroxy ends. It can also join DNA with 3′-phosphate ends to DNA with 5′-hydroxy ends, provided the DNA termini are unpaired [6]. The enzyme is found in members of all three kingdoms of life, and is essential in metazoa for the splicing of intron-containing tRNAs. The reaction follows a three-step mechanism with initial activation of the enzyme by GTP hydrolysis, forming a phosphoramide bond between the guanylate and a histidine residue. The guanylate group is transferred to the 3′-phosphate terminus of the substrate, forming the capped structure [DNA/RNA]-3′-(5′-diphosphoguanosine). When a suitable 5′-OH end is available, the enzyme catalyses an attack of the 5′-OH on the capped end to form a 3′-5′ phosphodiester splice junction, releasing the guanylate. When acting on an RNA 2′,3′-cyclic-phosphate, the enzyme catalyses an additional reaction, hydrolysing the cyclic phosphate to a 3′-phosphate [9]. The metazoan enzyme requires activating cofactors in order to achieve multiple turnover catalysis [8].

created 2017