Comparative analysis of the mating-type loci from Neurospora crassa and Sordaria macrospora: identification of novel transcribed ORFs.
The mating-type locus controls mating and sexual development in filamentous ascomycetes. In the heterothallic ascomycete Neurospora crassa, the genes that confer mating behavior comprise dissimilar DNA sequences (idiomorphs) in the mat a and mat A mating partners. In the homothallic fungus Sordaria macrospora, sequences corresponding to both idiomorphs are located contiguously in the mating-type locus, which contains one chimeric gene, Smt A-3, that includes sequences which are similar to sequences found at the mat A and mat a mating-type idiomorphs in N. crassa. In this study, we describe the comparative transcriptional analysis of the chimeric mating-type region of S. macrospora and the corresponding region of the N. crassa mat a idiomorph. By means of RT-PCR experiments, we identified novel intervening sequences in the mating-type loci of both ascomycetes and, hence, concluded that an additional ORF, encoding a putative polypeptide of 79 amino acids, is present in the N. crassa mat a idiomorph. Furthermore, our analysis revealed co-transcription of the novel gene with the mat a-1 gene in N. crassa. The same mode of transcription was found in the corresponding mating-type region of S. macrospora, where the chimeric Smt A-3 gene is co-transcribed with the mat a-specific Smt a-1 gene. Analysis of a Smt A-3 cDNA revealed optional splicing of two introns. We believe that this is the first report of co-transcription of protein-encoding nuclear genes in filamentous fungi. Possible functions of the novel ORFs in regulating mating-type gene expression are discussed.
Pöggeler
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Lehrstuhl für Allgemeine und Molekulare Botanik, Ruhr-Universität, Bochum, Germany.
Kück
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D017398:Alternative Splicing; D000595:Amino Acid Sequence; D001483:Base Sequence; D018076:DNA, Complementary / Q000235:genetics; D005800:Genes, Fungal; D049770:Genes, Mating Type, Fungal; D007438:Introns; D008969:Molecular Sequence Data; D009492:Neurospora crassa / Q000235:genetics*; D016366:Open Reading Frames; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D020037:Sordariales / Q000235:genetics*; D014158:Transcription, Genetic
D018076:DNA, Complementary; D012333:RNA, Messenger