title: The cyclic peptide synthetase catalyzing HC-toxin production in the filamentous fungus Cochliobolus carbonum is encoded by a 15.7-kilobase open reading frame.
abstract: Race 1 of Cochliobolus carbonum, a fungal plant pathogen, owes its exceptional virulence on certain genotypes of maize to the production of HC-toxin, a cyclic tetrapeptide. Production of HC-toxin is controlled by a single known gene, TOX2. Race 1, but not races that do not make HC-toxin, contains two copies of a 22-kilobase (kb) region of chromosomal DNA that is required for HC-toxin biosynthesis and hence virulence. We have sequenced this 22-kb region and here show that it contains an open reading frame of 15.7 kb that encodes a multifunctional cyclic peptide synthetase of potential M(r)574,620. This gene, called HTS1, apparently contains no introns. The predicted gene product, HC-toxin synthetase (HTS), contains four amino acid-binding (adenylate-forming) domains that are highly similar to those found in other cyclic peptide synthetases and other adenylate-binding enzymes. The DNA sequence encodes tryptic peptides derived from two HC-toxin biosynthetic enzymes, HC-toxin synthetase 1 (HTS-1) and HC-toxin synthetase 2 (HTS-2), indicating that these two enzymes exist in vivo as part of a single polypeptide. Consistent with this, in some enzyme preparations antibodies against the enzyme HTS-2, which was originally purified as a protein with a subunit M(r) of 160,000, recognize a protein with an estimated subunit M(r) greater than 480,000.
mesh_terms: D000591:Amino Acid Isomerases; D000595:Amino Acid Sequence; D001203:Ascomycota / Q000201:enzymology* / Q000235:genetics*; D001483:Base Sequence; D015153:Blotting, Western; D015825:Chromosomes, Fungal; D004271:DNA, Fungal / Q000235:genetics / Q000302:isolation & purification; D004591:Electrophoresis, Polyacrylamide Gel; D005800:Genes, Fungal; D006867:Hydrolases; D007527:Isoenzymes / Q000235:genetics*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009183:Mycotoxins / Q000096:biosynthesis*; D009838:Oligodeoxyribonucleotides; D016366:Open Reading Frames; D010446:Peptide Fragments / Q000302:isolation & purification; D010453:Peptide Synthases / Q000235:genetics*; D010456:Peptides, Cyclic / Q000096:biosynthesis*; D011061:Poly A / Q000235:genetics / Q000302:isolation & purification; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D012333:RNA, Messenger; D017386:Sequence Homology, Amino Acid
chemical_list: D004271:DNA, Fungal; D007527:Isoenzymes; D009183:Mycotoxins; D009838:Oligodeoxyribonucleotides; D010446:Peptide Fragments; D010456:Peptides, Cyclic; D012333:RNA, Messenger; C078713:HC-toxin synthetase 1; D011061:Poly A; D012313:RNA; C037654:HC toxin; D006867:Hydrolases; D000591:Amino Acid Isomerases; C078714:HC-toxin synthetase 2; D010453:Peptide Synthases