Golgi-mediated Glycosylation Determines Residency of the T2 RNase Rny1p in Saccharomyces cerevisiae

The role of glycosylation in the function of the T2 family of RNases is not well understood. In this work, we examined how glycosylation affects the progression of the T2 RNase Rny1p through the secretory pathway in Saccharomyces cerevisiae. We found that Rny1p requires entering into the ER first to become active and uses the adaptor protein Erv29p for packaging into COPII vesicles and transport to the Golgi apparatus. While inside the ER, Rny1p undergoes initial N-linked core glycosylation at four sites, N37, N70, N103 and N123. Rny1p transport to the Golgi results in the further attachment of high-glycans. Whereas modifications with glycans are dispensable for the nucleolytic activity of Rny1p, Golgi-mediated modifications are critical for its extracellular secretion. Failure of Golgi-specific glycosylation appears to direct Rny1p to the vacuole as an alternative destination and/or site of terminal degradation. These data reveal a previously unknown function of Golgi glycosylation in a T2 RNase as a sorting and secretion signal.