Analysis of genetic interactions between DHH1, SSD1 and ELM1 indicates their involvement in cellular morphology determination in Saccharomyces cerevisiae

The DHH1 gene of Saccharomyces cerevisiae belongs to a family of genes that encode highly conserved DEAD-box proteins commonly present in various eukaryotic organisms. Its precise function in yeast has not yet been well documented. To investigate its role in vivo, we constructed a DHH1 disruptant, characterized it genetically and searched for genes the mutations in which would cause synthetic lethality in combination with the DHH1 disruption. CDC28, ELM1 and SSD1 were thus found to be such candidates and we subsequently analysed their interactions. Mutations in ELM1 were previously reported to result in the elongation of cells. We confirmed this phenotype and observed in addition elongated bud formation in an Elm1p overproducing strain. Also, Elm1p fused with the green fluorescent protein (GFP) was found to be localized at the bud neck. These and other observations seem to suggest that Elm1p plays a role during cytokinesis in S. cerevisiae. The phenotypes of strains harbouring either Δdhh1 Δelm1 or ssd1-d Δelm1 were very similar to each other, showing abnormal cellular morphology and defects in cytokinesis and mitosis. Furthermore, DHH1 and SSD1 could functionally complement each other in the ade2 red colour pigment formation, hypersensitivity to SDS, growth on synthetic media and at high temperature. A triple mutant, Δdhh1 ssd1-d Δelm1, apparently had very fragile cell walls and could grow only in a medium supplemented with 1 M sorbitol.