Mutational Analysis of the pH Signal Transduction Component PalC ofAspergillus nidulansSupports Distant Similarity to BRO1 Domain Family Members

The alkaline ambient pH signal transduction pathway component PalC has no assigned molecular role. Therefore we attempted a gene-specific mutational analysis and obtained 55 new palC loss-of-function alleles including 24 single residue substitutions. Refined similarity searches reveal conserved PalC regions including one with convincing similarity to the BRO1 domain, denoted PCBROH, where clustering of mutational changes, including PCBROH key residue substitutions, supports its structural and/or functional importance. Since the BRO1 domain occurs in the multivesicular body (MVB) pathway protein Bro1/Vps31 and also the pH signal transduction protein PalA (Rim20), both of which interact with MVB component (ESCRT-III protein) Vps32/Snf7, this might reflect a further link between the pH response and endocytosis.