The PH domain of the yeast GEF Rom2p serves an essential function in vivo

Area of Science:

• Cell biology
• Molecular genetics
• Yeast biology

Background:

• The Pkc1p-MAP kinase pathway is crucial for yeast cell wall integrity and damage response.
• Rho1p is a key regulator activated by GDP/GTP exchange factors (GEFs).
• ROM2 encodes a GEF for Rho1p, but its precise role in the pathway is not fully understood.

Purpose of the Study:

• To identify novel upstream components of the Pkc1p-MAP kinase pathway.
• To characterize a newly identified mutant allele of the ROM2 gene (ubk1).
• To elucidate the function of the PH domain of Rom2p in vivo.

Main Methods:

• Yeast genetic screening to identify mutations affecting the Pkc1p-MAP kinase pathway.
• Complementation analysis using low- and high-copy-number vectors.
• Phenotypic analysis of rom2 deletion and mutant strains.
• Western blot analysis to assess Mpk1p phosphorylation levels.

Main Results:

• A new mutant allele, ubk1, was identified, encoding a truncated Rom2p lacking the PH domain.
• Deletion of the PH domain resulted in a phenotype indistinguishable from complete ROM2 deletion.
• The growth defect of rom2 mutants was strain-dependent.
• rom2 mutants exhibited elevated Mpk1p phosphorylation, suggesting normal MAP kinase activation.

Conclusions:

• The PH domain of Rom2p is essential for its function in vivo.
• The growth defect in rom2 mutants is not due to impaired Mpk1p activation.
• Rom2p has an unidentified function critical for yeast growth and cell wall integrity.