The PH domain of the yeast GEF Rom2p serves an essential function in vivo.
In a screen designed to identify new upstream components of the Pkc1p-MAP kinase signal transduction pathway that responds to cell wall damage in yeast, we identified a new mutant allele of the ROM2 gene, which encodes a GDP/GTP exchange factor that acts on Rho1p. This allele, originally termed ubk1 (upstream of Bck1p) encodes a truncated protein that lacks the putative PH domain. Complementation experiments showed that genes coding for several known components of the pathway are able to suppress the ubk1 mutation to various degrees when introduced on low- or high-copy-number vectors. Analysis of several rom2 mutants showed that mutants in which the PH domain is deleted result in a phenotype indistinguishable from that of a strain deleted for the entire gene, indicating that this domain fulfills an essential function in vivo. Furthermore, we found that the growth phenotype of rom2 mutants is highly dependent on the strain background. Surprisingly, analysis of the phosphorylation status of Mpk1p in these mutants showed an elevated level of doubly phosphorylated Mpk1 protein, indicating that the growth defect of rom2 mutants is not due to an inability to activate the MAP kinase module, but rather to lack of a function of the Rom2 protein that has yet to be identified precisely.
Lorberg
A
A
Institut für Mikrobiologie, Heinrich-Heine-Universität Düsseldorf, Universitätsstr.1, Geb. 26.12, D-40225 Düsseldorf, Germany.
Jacoby
J J
JJ
Schmitz
H P
HP
Heinisch
J J
JJ
D000483:Alleles; D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D002110:Caffeine / Q000494:pharmacology; D004271:DNA, Fungal / Q000032:analysis; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D007763:Lac Operon / Q000502:physiology; D008024:Ligands; D020935:MAP Kinase Signaling System; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation; D009995:Osmosis; D010641:Phenotype; D010766:Phosphorylation; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D015398:Signal Transduction; D014466:Ultraviolet Rays; D020741:rho GTP-Binding Proteins / Q000378:metabolism*
D004271:DNA, Fungal; D020662:Guanine Nucleotide Exchange Factors; D008024:Ligands; D029701:Saccharomyces cerevisiae Proteins; D002110:Caffeine; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; C051302:RHO1 protein, S cerevisiae; D020741:rho GTP-Binding Proteins