Isolation of extragenic suppressor mutations of the palI30 mutation of Aspergillus nidulans.

Daphne Smith, Bruce Dawson, Valerie Alexander, and Steven H. Denison.


The product of the pall gene of Aspergillus nidulans is a component of the ambient pH signal transduction pathway. To ensure production of alkaline-specific extracellular enzymes in alkaline environments and acid-specific extracellular enzymes in acid environments, this pathway modifies the pacC-encoded transcription factor in response to alkaline pH. Strains with mutations in the pall gene mimic growth in acidic conditions, showing (at pH 6.5) increased production of extracellular acid phosphatase, decreased production of alkaline phosphatase and increased sensitivity to molybdate in the growth medium. The pall gene encodes a protein with four putative transmembrane domains, and may therefore function as the pH sensor in the signal transduction pathway. In order to identify new components of this signalling pathway, we have isolated extragenic suppressor mutations of the pa1130 mutation. Following 4-NQO mutagenesis of spores, colonies were selected initially for growth on 17 mM sodium molybdate and secondarily for patterns of acid and alkaline phosphatase production more like wild type. Suppressor mutations have been identified in the pacC and pacX genes. Sequence analysis of these pacC mutations has identified amino acids which might be important in maintaining the closed form of PacC (L. Rainbow, J. Tilburn and H. N. Arst, Jr., unpublished). Mutations in the pacX gene are also able to suppress mutations in other pal genes and certain mutations in pacC (E. Bignell, J. Tilburn and H. N. Arst, Jr., unpublished).

abstract No: 

Fungal Genet. Newsl. 46 (Supl):

Full conference title: 

Fungal Genetics Conference 20th
    • Fungal Genetics Conference 20th (1999)