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

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

RNA containing adenosine-cytidine + H2O = an [RNA fragment]-3'-cytidine-3'-phosphate + a 5'-a hydroxy-adenosine -3'-[RNA fragment] (overall reaction);
(1a) RNA containing adenosine-cytidine = an [RNA fragment]-3'-cytidine-2',3'-cyclophosphate + a 5'-a hydroxy-adenosine -3'-[RNA fragment];
(1b) an [RNA fragment]-3'-cytidine-2',3'-cyclophosphate + H2O = an [RNA fragment]-3'-cytidine-3'-phosphate

RNA containing adenosine-cytidine;
H2O [CPD:C00001];
[RNA fragment]-3'-cytidine-2',3'-cyclophosphate

Preference for cleavage at Cp-A bonds. Homopolymers of A, U or G are not hydrolysed. CpG bonds are hydrolysed less well and there is no detectable hydrolysis between two purines or two pyrimidines. The enzyme catalyses a two-stage endonucleolytic cleavage. The first reaction produces 5'-hydroxy-phosphooligonucletides and 3'-phosphooligonucleotides ending a 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 4.6.1.21 created 1978 as EC 3.1.27.6, modified 1981, transferred 2018 to 4.6.1.21

1  [PMID:5432809]

Levy CC, Goldman P.

Residue specificity of a ribonuclease which hydrolyzes polycytidylic acid.

J Biol Chem 245:3257-62 (1970)

2  [PMID:4719125]

Marotta CA, Levy CC, Weissman SM, Varricchio F.

Preferred sites of digestion of a ribonuclease from Enterobacter sp. in the sequence analysis of Bacillus stearothermophilus 5S ribonucleic acid.

Biochemistry 12:2901-4 (1973)
DOI:10.1021/bi00739a020