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). 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 sessil bond, respectively. This CD includes the eukaryotic RNase T2 family members.
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