Abstract
The level of aflatoxin accumulation in the filamentous fungus Aspergillus parasiticus is modulated by a variety of environmental cues. The presence of glucose (a preferred carbon source) in liquid and solid glucose minimal salts (GMS) growth media strongly stimulated aflatoxin accumulation. Peptone (a non-preferred carbon source) in peptone minimal salts (PMS) media stimulated only low levels of aflatoxin accumulation. Glucose stimulated transcription of the aflatoxin structural genes ver-1 and nor-1 to similar intermediate levels in liquid GMS, while on solid media, ver-1 transcription was stimulated to 20-fold higher levels than nor-1. PMS liquid and solid media stimulated very low or non-detectable levels of transcription of both genes. Electropheretic mobility shift analysis using a nor-1 promoter fragment (norR) and A. parasiticus cell protein extracts revealed specific DNA-protein complexes of different mobility on GMS and PMS solid and liquid media. An imperfect cAMP-response element, CRE1, was identified in norR that mediated formation of the specific DNA-protein complexes. Mutation in CRE1 or AflR1 (AflR cis-acting site) caused up to a 3-fold decrease in cAMP-mediated stimulation of nor-1 promoter activity on GMS agar. South-Western blot analysis identified a 32-kDa protein that specifically bound to norR. p32 could be co-immunoprecipitated by anti-AflR antibody and co-purified with an AflR-maltose-binding protein fusion demonstrating a physical interaction between AflR and p32 in vitro. We hypothesize that p32 assists AflR in binding to the nor-1 promoter, thereby modulating nor-1 gene expression in response to environmental cues.
Original language | English (US) |
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Pages (from-to) | 27428-27439 |
Number of pages | 12 |
Journal | Journal of Biological Chemistry |
Volume | 279 |
Issue number | 26 |
DOIs | |
State | Published - Jun 25 2004 |
Externally published | Yes |
ASJC Scopus subject areas
- Biochemistry
- Molecular Biology
- Cell Biology