Abstract, Larson and Nuss, EMBO J. 13(1994), 5616-5623.

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Altered Transcriptional Response to Nutrient Availability in Hypovirus-Infected
Chestnut Blight Fungus

EMBO J.  13(1994), 5616-5623

Thomas G. Larson and Donald L. Nuss

Roche Institute of Molecular Biology
Roche Research Center
Nutley, NJ 07110, USA


The gene lac-1, encoding the enzyme laccase, is one of several genes 
of the chestnut blight fungus, Cryphonectria parasitica, that are suppressed 
by virulence-attenuating mycoviruses of the genus Hypovirus.  Two 
antagonistic regulatory pathways have been shown to govern the activity 
of the lac-1 promoter: a positive pathway that stimulates transcription 
and a negative pathway that represses transcription.  We now report that
these two regulatory pathways respond independently to specific changes 
in the nutritional environment.  These newly defined conditions were used
to confirm that the hypovirus suppresses the activity of the positive
regulatory pathway and to implicate calmodulin and calcineurin as components
of the signal transduction cascades regulating lac-1 transcription.
Significantly, lac-1 transcript accumulation was shown to be affected 
by amino acid availability.  Further analysis revealed that transcriptional
repression mediated by the negative regulatory pathway is relieved under
conditions of amino acid deprivation.  Thus, by blocking the positive pathway,
hypovirus infection prevents increased lac-1 transcript accumulation in
response to amino acid deficiency.  These observations are consistent with 
the hypothesis that hypoviruses alter the transcriptional response of the 
host fungus to changes in nutritional availability.  

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