Signal transduction through the Rim101p pH-response pathway.
Wenjie Xu, Aaron Mitchell
Integrated Program in CMBS,
Columbia University, 701 West 168 street, New York, NY 10032, USA
In
S. cerevisiae, the developmental processes of sporulation and
haploid invasive growth are stimulated at neutral or alkaline pH. The
genes RIM8, RIM9, RIM13(aka CPL1), RIM20, RIM21(aka
RIM30) and RIM101 lie in a conserved pathway that governs
pH responses in many fungi. Rim101p is the downstream component of the
pathway; it is a zinc-finger transcription factor that is activated by
proteolytic cleavage of its ~100-residue C-terminal region (CTR). Other
Rim proteins are required for Rim101p cleavage. Rim13p/Cpl1p is a
cysteine protease that probably cleaves the CTR directly. Our recent
studies show that Rim20p interacts with the Rim101p CTR, and a recent
genome-wide two-hybrid study (Ito et al., PNAS 98:4569) indicates that
Rim20p interacts with Snf7p and that Snf7p interacts with Rim13p. Thus
we have suggested that the Rim20p-Snf7p complex forms a scaffold for
juxtaposition of the Rim101p CTR and Rim13p. We have confirmed the
Rim20p-Snf7p interaction, and verified two predictions of our
hypothesis: 1. A snf7 deletion mutant is defective in Rim101p cleavage
and in Rim101p-dependent functions. 2. The Rim101p CTR is sufficient to
direct its cleavage when fused to Ura3p; cleavage depends upon Rim13p,
Rim20p, and Snf7p. Snf7p is required for fusion of endocytic vesicles
with the vacuole, but Rim101p and other Rim products are not. Therefore,
we believe that Snf7p has two distinct cellular functions.
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