| Popis: |
Many yeast and fungi grow over a wide pH range, and their gene expression is tailored to the pH of their environment. A conserved ambient pH signal transduction pathway has been evidenced in both ascomycetous yeasts and filamentous fungi, called Rim or Pal, respectively. The transcriptional factor Rim101p/PacC is activated by a proteolytic C-terminal processing in response to alkaline ambient pH. In A. nidulans and probably in Y. lipolytica, this processing occurs in two steps, the first one being pH signal dependent and the second one proteasomal. The Rim101p/PacC truncated form is able to activate alkaline pH-responsive genes and to repress acid-induced genes. The Rim/Pal pathway involves both a plasma membrane complex including the 7-TMD protein and putative pH sensor Rim21p/PalH, the 3-TMD protein and putative assistant of Rim21p/PalH localization Rim9p/PalI, and the arrestin-like protein Rim8p/palF, and an ESCRT-associated Rim101 processing machinery which comprises, besides Rim101p/PacC, three interactors of the ESCRT-III-subunit Snf7p/Vps32p: the calpain-like signalling protease Rim13p/PalB, a scaffold Rim20p/PalA, and YlRim23p/PalC. According to the current model, in response to alkaline ambient pH, the interaction of Rim21/PalH with Rim8p/PalF bound to the ESCRT-I subunit Vps23p would promote the ESCRT machinery recruitment to the plasma membrane, like in retroviral budding. And the interaction of the ESCRT-III-subunit Snf7 with both Rim13p/PalB and Rim20p/PalA bound to Rim101p/PacC would trigger the pH-signal-dependent proteolytic processing of Rim101/PacC. Evolutionary conserved mechanisms would control the recruitment of the ESCRT machinery to Rim/Pal proteins in fungi and to retroviral Gag proteins in animal cells. |
