Identification of Yeast Protein Sequences With Similarity to the ESCRT-III Protein Snf7

Endosomal sorting complex required for transport (ESCRT-III) is a membrane remodeling complex involved in a large number of cellular processes. It appears to perform an essential function in eukaryotes, since to date no eukaryotic organism completely devoid of ESCRT-III has been found. Yet, yeast cells with a deletion of all eight known ESCRT-III genes are viable. We therefore searched for new, previously undiscovered ESCRT-III like proteins in yeast. HHPred uncovered several proteins with similarity to Snf7. The similarity was mostly restricted to the α1-α2 hairpin region of Snf7. A conserved pattern of amino acids was detected in this region. One of the proteins with an ESCRT-III like sequence pattern, which strikingly resembled Snf7 in its secondary structure, was studied more closely. We named the protein encoded by ORF YPL199c Etl1 (ESCRT-three-like 1). Etl1 is palmitoylated and localizes to the plasma membrane. In contrast to other palmitoylated proteins, Etl1 does not appear to be associated with lipid rafts, since it could be easily extracted from the membrane by Triton X-100 treatment. When ETL1 was deleted in the octuple ESCRT-III deletion background, the yeast cells were still viable. So far, despite a number of experiments, a bona fide ESCRT-III function could not be demonstrated for Etl1.