Regulation of cyclic peptide biosynthesis and pathogenicity in Cochliobolus carbonum by TOXEp, a novel protein with a bZIP basic DNA-binding motif and four ankyrin repeats |
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Authors: | J-H Ahn and J D Walton |
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Institution: | (1) Department of Energy-Plant Research Laboratory Michigan State University, E. Lansing Michigan 48824,USA e-mail: walton@pilot.msu.edu Tel: +1-517-353-4885, Fax: +1-517-353-9168, US |
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Abstract: | HC-toxin is an epoxide-containing cyclic tetrapeptide that is a critical virulence determinant in the pathogenic interaction
between the filamentous fungus Cochliobolus carbonum and maize. HC-toxin exerts a potent cytostatic effect on plant and animal cells by inhibiting histone deacetylase. The biosynthesis
of HC-toxin by C. carbonum is controlled by a complex genetic locus, TOX2, that contains multiple, duplicated copies of genes encoding export and biosynthetic enzymes. A new gene in the TOX2 complex, TOXE, has now been isolated. Mutation of TOXE by targeted gene disruption has no effect on growth and sporulation but abolishes HC-toxin production and pathogenicity.
TOXE is required for the expression of three genes with a known or putative role in HC-toxin production, but is not required for
expression of HTS1, which encodes the large, multifunctional peptide synthetase that is the central enzyme in HC-toxin biosynthesis. At its
N-terminus, TOXEp has a bZIP basic DNA binding domain, but it does not contain any discernible leucine zipper or helix-loop-helix.
At its carboxy terminus, TOXEp contains four ankyrin repeats. In having these two common regulatory motifs in a single polypeptide,
TOXEp appears to represent a novel class of regulatory protein. TOXE is present only in HC-toxin-producing (Tox2+) isolates of C. carbonum. Most Tox2+ isolates have two copies; in strain SB111, one copy of TOXE is on the same 3.5-Mb chromosome that contains all of the other genes known to be involved in HC-toxin biosynthesis, and
the second copy of TOXE is on a 0.7-Mb chromosome.
Received: 20 April 1998 / Accepted: 21 September 1998 |
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Keywords: | Cochliobolus carbonum HC-toxin |
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