Identification of ESCRT-III like protein sequences in yeast

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, it is not associated with lipid rafts. When ETL1 was deleted in the octuple ESCRT-III deletion background, the yeast cells were still viable. However, despite a number of experiments, we do not have evidence at present that Etl1 is part of an alternative ESCRT-III complex.