Signaling of Ambient pH in Aspergillus Involves a Cysteine Protease

Steven H Denison,Margarita Orejas,Herbert N Arst

doi:10.1074/jbc.270.48.28519

Abstract

In Aspergillus nidulans, the regulation of gene expression in response to changes in ambient pH is mediated by the PacC zinc finger transcriptional regulator. At alkaline ambient pH, PacC is proteolytically processed to a functional form serving as an activator of alkaline-expressed genes and a repressor of acid-expressed genes. This activation of PacC occurs in response to a signal mediated by the products of the pal genes. Thus, the products of the palA, -B, -C, -F, -H, and -I genes constitute an alkaline ambient pH signal transduction pathway. How the pal signal transduction pathway senses ambient pH and transduces a signal to trigger PacC processing is a fascinating unresolved problem. We have cloned and sequenced the palB gene. The predicted palB gene product has similarity to the catalytic domain of the calpain family of calcium-activated cysteine proteases. We have shown, however, that the PalB protein does not catalyze the final step of proteolytic processing of PacC.

Highlights

In Aspergillus nidulans, the regulation of gene expression in response to changes in ambient pH is mediated by the PacC zinc finger transcriptional regulator
Transfor-The ascomycete Aspergillus nidulans, like many other microorganisms, grows over a wide pH range [1, 2]. Crucial to this physiological versatility, A. nidulans has a regulatory system to ensure that gene products that function beyond cell boundaries, such as permeases and extracellular enzymes, are only synthesized at pHs at which they can function effectively so that, for example, acid phosphatase is secreted in acidic environments and alkaline phosphatase in alkaline environments [1, 3, 4]
All 104 progeny analyzed were palBϩ, and the argBϩ and chaA1 markers showed 8% recombination, consistent with the linkage [12] between palB and chaA. This and the result that the larger, overlapping SphI restriction fragment rescued at a higher frequency suggested that the entire palB gene might not be contained within the BamHI fragment and that the BamHI site within the SphI fragment might be within the palB gene (Fig. 1)

Summary

Introduction

In Aspergillus nidulans, the regulation of gene expression in response to changes in ambient pH is mediated by the PacC zinc finger transcriptional regulator. At alkaline ambient pH, PacC is proteolytically processed to a functional form serving as an activator of alkalineexpressed genes and a repressor of acid-expressed genes. This activation of PacC occurs in response to a signal mediated by the products of the pal genes. The predicted palB gene product has similarity to the catalytic domain of the calpain family of calcium-activated cysteine proteases. We have cloned the palB gene and shown that the predicted PalB protein has sequence similarity to the catalytic domain of the calpain family of calcium-activated cysteine proteases. A cysteine protease is a component of the alkaline ambient pH signal transduction pathway in Aspergillus

Methods

Results

Conclusion