Identification of SPT14/CWH6 as the yeast homologue of hPIG-A, a gene involved in the biosynthesis of GPI anchors.

Cwh6 is a temperature-sensitive cell wall mutant of Saccharomyces cerevisiae. CWH6 was found to be identical to SPT14, a gene that is highly homologous to both human PIG-A and to RFAK from Salmonella typhimurium. PIG-A and RFAK are involved in transferring N-acetylglucosamine to, respectively, a GPI anchor precursor and to lipopolysaccharides. Because cell walls of cwh6 are greatly reduced in mannose, and because some cell wall proteins are known to be incorporated into the cell wall through a GPI-anchor dependent mechanism, we propose that Spt14p/Cwh6p is involved in transferring N-acetylglucosamine to a precursor of GPI anchors. We further propose that the majority of cell wall proteins are incorporated into the cell wall through a GPI anchor.