Characterization of Rny1, the Saccharomyces cerevisiae member of the T2 RNase family of RNases:: Unexpected functions for ancient enzymes?

The T-2 family of nonspecific endoribonucleases (EC 3.1.27.1) is a widespread family of RNases found in every organism examined thus far. Most T-2 enzymes are secretory RNases and therefore are found extracellularly or in compartments of the endomembrane system that would minimize their contact with cellular RNA. Although the biological functions of various T-2 RNases have been postulated on the basis of enzyme location or gene expression patterns, the cellular roles of these enzymes are generally unknown. In the present work, we characterized Rny1, the only T-2 RNase in Saccharomyces cerevisiae. Rny1 was found to be an active, secreted RNase whose gene expression is controlled by heat shock and osmotic stress. Inactivation of RNY1 leads to unusually large cells that are temperature-sensitive for growth. These phenotypes can be complemented not only by RNY1 but also by both structurally related and unrelated secretory RNases. Additionally, the complementation depends on RNase activity. When coupled with a recent report on the effect of specific RNAs on membrane permeability [Khvorova, A., Kwak, Y-G., Tamkun, M., Majerfeld, I. & Yarus, M. (1999) Proc. NatI. Acad. Sci. USA 96, 10649-10654], our work suggests an unexpected role for Rny1 and possibly other secretory RNases. These enzymes may regulate membrane permeability or stability, a hypothesis that could present an alternative perspective for understanding their functions.