InterPro domain: IPR001568

The fungal ribonucleases T2 from Aspergillus oryzae, M from Aspergillus saitoi and Rh from Rhizopus niveus are structurally and functionally related 30 Kd glycoproteins [ 1 ] that cleave the 3'-5' internucleotide linkage of RNA via a nucleotide 2',3'-cyclic phosphate intermediate ( 3.1.27.1 ). Two histidines residues have been shown [ 2 , 3 ] to be involved in the catalytic mechanism of RNase T2 and Rh. These residues and the region around them are highly conserved in a number of other RNAses that have been found to be evolutionary related to these fungal enzymes.

Ribonuclease T2 (RNase T2) is a widespread family of secreted RNases found in every organism examined thus far. This family includes RNase Rh, RNase MC1, RNase LE, and self-incompatibility RNases (S-RNases) [ 4 , 5 , 6 , 7 , 8 ]. Plant T2 RNases are expressed during leaf senescence in order to scavenge phosphate from ribonucleotides. They are also expressed in response to wounding or pathogen invasion. S-RNases are thought to prevent self-fertilization by acting as selective cytotoxins of "self" pollen. Generally, RNases have two distinct binding sites: the primary site (B1 site) and the subsite (B2 site), for nucleotides located at the 5'- and 3'- terminal ends of the sissile bond, respectively.

1. Primary structure of a base non-specific and adenylic acid preferential ribonuclease from Aspergillus saitoi. J. Biochem. 108, 303-10
2. Identification of two essential histidine residues of ribonuclease T2 from Aspergillus oryzae. Eur. J. Biochem. 187, 255-62
3. Crystal and molecular structure of RNase Rh, a new class of microbial ribonuclease from Rhizopus niveus. FEBS Lett. 306, 189-92
4. Ribonucleases from T2 family. Crit. Rev. Microbiol. 28, 79-122
5. Ribonuclease T2. Meth. Enzymol. 341, 42-55
6. Crystal structure of a ribonuclease from the seeds of bitter gourd (Momordica charantia) at 1.75 A resolution. Biochim. Biophys. Acta 1433, 253-60
7. Crystal structures of the ribonuclease MC1 mutants N71T and N71S in complex with 5'-GMP: structural basis for alterations in substrate specificity. Biochemistry 42, 5270-8
8. Characterization of Rny1, the Saccharomyces cerevisiae member of the T2 RNase family of RNases: unexpected functions for ancient enzymes? Proc. Natl. Acad. Sci. U.S.A. 98, 1018-23