Temperature-sensitive cdc1(ts) mutants are reported to stop the cell cycle upon a shift to 30°C in early G2, that is, as small budded cells having completed DNA replication but unable to duplicate the spindle pole body. A recent report showed that PGAP5, a human homologue of CDC1, acts as a phosphodiesterase removing an ethanolamine phosphate (EtN-P) from mannose 2 of the glycosylphosphatidylinositol (GPI) anchor, thus permitting efficient endoplasmic reticulum (ER)-to-Golgi transport of GPI proteins. We find that the essential CDC1 gene can be deleted in mcd4∆ cells, which do not attach EtN-P to mannose 1 of the GPI anchor, suggesting that Cdc1 removes the EtN-P added by Mcd4. Cdc1-314(ts) mutants do not accumulate GPI proteins in the ER but have a partial secretion block later in the secretory pathway. Growth tests and the genetic interaction profile of cdc1-314(ts) pinpoint a distinct cell wall defect. Osmotic support restores GPI protein secretion and actin polarization but not growth. Cell walls of cdc1-314(ts) mutants contain large amounts of GPI proteins that are easily released by β-glucanases and not attached to cell wall β1,6-glucans and that retain their original GPI anchor lipid. This suggests that the presumed transglycosidases Dfg5 and Dcw1 of cdc1-314(ts) transfer GPI proteins to cell wall β1,6-glucans inefficiently.
© 2014 Vazquez et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).