The localization change of Ybr078w/Ecm33, a yeast GPI-associated protein,from the plasma membrane to the cell wall,affecting the cellular function

The YBR078W/ECM33 gene of Saccharomyces cerevisiae encodes a glycosylphosphatidylinositol (GPI)-attached protein and its disruptant strain exhibited a temperature-sensitive (ts) growth defect. A HA-tagged Ybr078w protein, which complemented the ts growth phenotype of the ybr078wdelta strain, was predominantly located on the plasma membrane by GPI anchoring. To examine the requirement of the GPI anchoring on the plasma membrane for the function, the omega-minus region of Ybr078w was replaced with those of Ydr534c/Fit1 and Ynl327w/Egt2, which are known as GPI-dependent cell wall proteins. The replacement induced the change in localization of the mutant proteins from the plasma membrane to the cell wall and the mutant proteins lost the function to complement the ts cell growth defect of the ybr078wdelta strain. In addition, a similar result was obtained in a mutant protein, where the authentic SKKSK sequence at the omega-5 to omega-1 site of Ybr078w was replaced with a synthetic ISSYS sequence. It is concluded that the GPI anchoring on the plasma membrane is required for the Ybr078w function.