T2 Family ribonucleases: ancient enzymes with diverse roles - PubMed

Although T2 ribonucleases exhibit a conserved core structure, these enzymes perform diverse functions. (a) Scavenging of extracellular or intracellular RNAs.

Extracellular RNA

. Plants secrete RNaseT2 proteins (red), such as tomato RNase LE, during phosphate starvation; the T2 proteins might scavenge extracellular RNA and recycle RNA components to the cell [–39].

Intracellular RNA

. During autophagy, protein aggregates are internalized by autophagosomes and taken up by the vacuole/lysosome [41, 43]. Intracellular RNA, as part of ribonucleoprotein complexes (RNPs; blue) such as P-granules [43], might be degraded in this manner by RNaseT2 proteins within the vacuole/lysosome. (b)Plant S-RNases and coordination of self-incompatibility. A model for compartmentalized control of S-RNase activity is depicted. S-RNases are secreted by pistil cells to the extracellular matrix (ECM) wherein they can be internalized to the cytosol of the pollen tube and have been shown to localize to a vacuole-like compartment [5, 59, 60, 75]. This compartment is maintained if pollen is compatible, but disintegration of the compartment occurs late in incompatible pollination, perhaps enabling the degradation of pollen RNAs and blocking pollen tube development [5]. Pistil factors required for decompartmentalization and the pollen protein SLF are not shown for simplicity. (c) Pestiviral envelope glycoprotein, E^rns, and cytotoxicity. The E^rns protein found in pestiviruses is secreted by its host’s infected cells and internalized by host immune cells in a receptor-independent manner through its positive charge (C-terminus) [31, 51]. There, it depletes host immune cells through both catalytic-dependent and –independent functions [–56]. (d) The budding yeast RNaseT2 protein, Rny1, and the oxidative stress response. Rny1 localizes to the vacuole in unstressed cells, and oxidative stress causes its release into the cytoplasm where it cleaves tRNAs and rRNAs [4, 67]. Rny1 also possesses a catalytic-independent activity which regulates cellular viability during oxidative stress [4]. ER: endoplasmic reticulum