Lyases;
Phosphorus-oxygen lyases;
Phosphorus-oxygen lyases (only sub-subclass identified to date)
BRITE hierarchy

[pre-mRNA]-guanosine-adenosine 5'-hydroxy-guanosine-ribonucleotide-3'-[RNA fragment]-lyase (cyclicizing; [RNA fragment]-3'- adenosine -2',3'-cyclophosphate-forming and hydrolysing)

a [pre-mRNA]-containing guanosine-adenosine + H2O = a 5' hydroxy-guanosine-[pre-mRNA fragment] + a [pre-mRNA fragment]-3'-adenosine-3'-phosphate (overall reaction);
(1a) a [pre-mRNA]-containing guanosine-adenosine + H2O = a 5' hydroxy-guanosine-[pre-mRNA fragment] + a [pre-mRNA fragment]-adenosine-2',3'-cyclophosphate;
(1b) a [pre-mRNA fragment]- adenosine-2',3'-cyclophosphate + H2O = a [pre-mRNAfragment]-3'-adenosine-3'-phosphate

[pre-mRNA]-containing guanosine-adenosine;
H2O [CPD:C00001];
[pre-mRNA fragment]- adenosine-2',3'-cyclophosphate

The enzyme from bacteriophage T4 cleaves early mRNAs between Ap and Gp at one specific specific GpGpApGp site, favouring their further transition to middle-phase mRNA. The activity is enhanced by Ribosomal S1 protein. The enzyme catalyses a two-stage endonucleolytic cleavage. The first reaction produces 5'-hydroxy-phosphooligonucletides and 3'-phosphooligonucleotides ending with 2',3'-cyclic phosphodiester, which are released from the enzyme. The enzyme then hydrolyses these cyclic compounds in a second reaction that takes place only when all the susceptible 3',5'-phosphodiester bonds have been cyclised. The second reaction is a reversal of the first reaction using the hydroxyl group of water instead of the 5'-hydroxyl group of ribose. The overall process is that of a phosphorus-oxygen lyase followed by hydrolysis to form the 3'-nucleotides.

EC 4.6.1.25 created 2020

1  [PMID:10764573]

Sanson B, Hu RM, Troitskayadagger E, Mathy N, Uzan M

Endoribonuclease RegB from bacteriophage T4 is necessary for the degradation of early but not middle or late mRNAs.

J Mol Biol 297:1063-74 (2000)
DOI:10.1006/jmbi.2000.3626

2  [PMID:12771201]

Saida F, Uzan M, Bontems F

The phage T4 restriction endoribonuclease RegB: a cyclizing enzyme that requires  two histidines to be fully active.

Nucleic Acids Res 31:2751-8 (2003)
DOI:10.1093/nar/gkg377

3  [PMID:17046813]

Odaert B, Saida F, Aliprandi P, Durand S, Crechet JB, Guerois R, Laalami S, Uzan M, Bontems F

Structural and functional studies of RegB, a new member of a family of sequence-specific ribonucleases involved in mRNA inactivation on the ribosome.

J Biol Chem 282:2019-28 (2007)
DOI:10.1074/jbc.M608271200

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