Functional genomics of monensin sensitivity in yeast: implications for post-Golgi traffic and vacuolar H+-ATPase function
Gustavsson M, Barmark G, Larsson J, Murén E, Ronne H
Molecular Genetics and Genomics (2008)
Category: ions, vacuole, yeast-misc ¤ Added: Apr 02, 2009 ¤ Rating: ◊◊
We have screened a complete collection of yeast knockout mutants for sensitivity to monensin, an ionophore that interferes with intracellular transport. A total of 63 sensitive strains were found. Most of the strains were deleted for genes involved in post-Golgi traYc, with an emphasis on vacuolar biogenesis. A high correlation was thus seen with VPS and VAM genes, but there were also signiWcant diVerences between the three sets of genes. A weaker correlation was seen with sensitivity to NaCl, in particular rate of growth eVects. Interestingly, all 14 genes encoding subunits of the vacuolar H+-ATPase (V-ATPase) were absent in our screen, even though they appeared in the VPS or VAM screens. All monensin-sensitive mutants that could be tested interact synthetically with a deletion of the A subunit of the V-ATPase, Vma1. Synthetic lethality was limited to mutations aVecting endocytosis or retrograde transport to Golgi. In addition, vma1 was epistatic over the monensin sensitivity of vacuolar transport mutants, but not endocytosis mutants. Deletions of the two isoforms of the V-ATPase a subunit, Vph1 and Stv1 had opposite eVects on the monensin sensitivity of a ypt7 mutant. These Wndings are consistent with a model where monensin inhibits growth by interfering with the maintenance of an acidic pH in the late secretory pathway. The synthetic lethality of vma1 with mutations aVecting retrograde transport to the Golgi further suggests that it is in the late Golgi that a low pH must be maintained.