IUBMB Enzyme Nomenclature


Accepted name: bacteriophage T4 restriction endoribonuclease RegB

Reaction: a [pre-mRNA]-containing guanosine-adenosine + H2O = a 5' hydroxy-guanosine-[pre-mRNA fragment] + a [pre-mRNA fragment]-3'-adenosine-3'-phosphate
(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

Other name(s): RegB

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

Comments: 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.

Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:


1. Sanson, B., Hu, R.M., Troitskayadagger, E., Mathy, N. and Uzan, M. Endoribonuclease RegB from bacteriophage T4 is necessary for the degradation of early but not middle or late mRNAs. J. Mol. Biol. 297 (2000) 1063-1074. [PMID: 10764573]

2. Saida, F., Uzan, M. and Bontems, F. The phage T4 restriction endoribonuclease RegB: a cyclizing enzyme that requires two histidines to be fully active. Nucleic Acids Res. 31 (2003) 2751-2758. [PMID: 12771201]

3. Odaert, B., Saida, F., Aliprandi, P., Durand, S., Crechet, J.B., Guerois, R., Laalami, S., Uzan, M. and 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 (2007) 2019-2028. [PMID: 17046813]

[EC created 2020]

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