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

Abstract

We have cloned the palA gene of Aspergillus nidulans, one of six genes participating in ambient pH signal transduction in a regulatory circuit mediating pH regulation of gene expression. The derived 798-residue PalA protein is 29.4% identical over its entire length to a hypothetical protein from the nematode Caenorhabditis elegans and also has possible yeast homologs.In the filamentous fungus Aspergillus nidulans, as in many other microorganisms, the syntheses of a number of permeases, secreted enzymes, and exported metabolites are appropriately regulated by ambient pH (3). For example, acid phosphatase and the acid-pH-optimum ␥-aminobutyrate permease are synthesized preferentially in acidic media, whereas alkaline phosphatase and penicillin are synthesized preferentially in alkaline media (3,7,18). 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 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). Here, we report the cloning and sequence of palA. Amino acid sequence similarity strongly suggests that the palA gene product has a homolog in the nematode Caenorhabditis elegans. It also has possible homologs in the yeasts Schizosaccharomyces pombe and Saccharomyces cerevisiae.The palA gene was cloned with linkage group III (containing palA) clones from a chromosome-allocated wild-type A. nidulans cosmid library (2) and pILJ16 (11) and by identification of palA ϩ cotransformants by their ability to grow on pH 8 medium (3-5) among argB ϩ transformants of a strain of genotype biA1 yA2 wA3 argB2 areA49 palA1. palA1-rescuing activity was found in cosmid W28H12 and further localized to a 5-kb XbaIXhoI fragment (Fig. 1A). To confirm that this fragment contains the palA gene itself rather than a gene associated with a fortuitous suppressor activity, strains carrying either of two

Paraptosis: mediation by MAP kinases and inhibition by AIP-1/Alix

“…35,36 Our results are consistent with and complement these results, suggesting a novel function for AIP1/Alix as an inhibitor of paraptosis.…”

Regulation of Gene Expression by Ambient pH in Filamentous Fungi and Yeasts

“…Mutations in these six pal genes are in all cases recessive and hypostatic to (i.e., phenotypically masked or suppressed by) the vast majority of pacC mutations (3,17,95; L. A. Rainbow, J. Tilburn, and H. N. Arst, Jr., unpublished data). Null mutations in pacC and the six pal genes lead to strong acidity mimicry (31,32,90,91,122; H. J. Bussink, M. A. Peñalva, and H. N. Arst, Jr., unpublished data).…”

The RhoA-binding protein, Rhophilin-2, Regulates Actin Cytoskeleton Organization

“…Although the biological and biochemical functions of Bro1 domains are not known, the first Bro1-containing protein identified, from Saccharomyces cerevisiae, is linked genetically to a protein kinase C signaling pathway that regulates osmoregulation (36). Bro1 domains have been identified subsequently in a variety of other signaling proteins, including a phosphatase (37), proteins involved in cell death (38,39), pH regulation (40), and oocyte maturation (41).…”