A signal comprising a basic cluster and an amphipathic α-helix interacts with lipids and is required for the transport of Ist2 to the yeast cortical ER

The yeast integral plasma membrane protein Ist2 belongs to a group of membrane proteins which are synthesized from localized mRNAs. The protein reaches the plasma membrane via the ER on a route operating independently of the classical secretory pathway. We have identified a complex peptide-sorting signal located at the extreme C-terminus. This sorting signal operates independently of targeting information in IST2 mRNA and sorting to the plasma membrane does not require She-mediated mRNA transport into daughter cells. Based on these results, we suggest a posttranslational mechanism, which leads to the concentration of Ist2 -via multimerization -at ER sites, followed by direct transport to the plasma membrane. This novel mechanism operates downstream of IST2 mRNA localization.

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