Signaling of Ambient pH in Aspergillus Involves a Cysteine Protease

Characterization of the pH signal transduction pathway gene palA of Aspergillus nidulans and identification of possible homologs

“…We have previously shown that the palB gene product is likely to be a cysteine protease of the calpain family, albeit not the protease responsible for the final conversion of PacC to its functional form (5). Here, we report the cloning and sequence of palA.…”

“…pH regulation of gene expression is mediated by the zinc finger transcription factor PacC, whose 73-kDa full-length translation product is proteolyzed to yield a 29-kDa N-terminal fragment able to activate transcription of genes expressed at alkaline pH and prevent transcription of genes expressed at acid pH (15,17,19). The products of six genes, palA, -B, -C, -F, -H, and -I, form a signal transduction pathway through which alkaline ambient pH is able to elicit the conversion of the full-length form of PacC to the functional proteolyzed form (1,3,5,15,19). Loss-of-function mutations in these pal genes prevent this proteolytic conversion and mimic the effects of growth at acidic pH (1,3,5,7,15,18).…”

“…The products of six genes, palA, -B, -C, -F, -H, and -I, form a signal transduction pathway through which alkaline ambient pH is able to elicit the conversion of the full-length form of PacC to the functional proteolyzed form (1,3,5,15,19). Loss-of-function mutations in these pal genes prevent this proteolytic conversion and mimic the effects of growth at acidic pH (1,3,5,7,15,18).The mechanism of ambient pH signal transduction is an intriguing subject of scientific and biotechnological importance. We have previously shown that the palB gene product is likely to be a cysteine protease of the calpain family, albeit not the protease responsible for the final conversion of PacC to its functional form (5).…”

Physiological Involvement in pH Signaling of Vps24-mediated Recruitment of Aspergillus PalB Cysteine Protease to ESCRT-III

“…PacC 27 is a transcriptional activator of alkaline-expressed genes and a repressor of acid-expressed genes (13,14). The alkaline ambient pH-dependent conversion of PacC 72 into PacC 53 is almost certainly catalyzed by the calpain-like cysteine protease PalB (10,15,16) (see Refs. 7, 8, 17 for reviews).…”

Evidence for the Direct Involvement of the Proteasome in the Proteolytic Processing of the Aspergillus nidulans Zinc Finger Transcription Factor PacC

“…1A). The signaling protease is almost certainly the cysteine protease PalB (25,26). The subject of this work is the identity of the "processing" protease mediating the second step.…”