Pöggeler S, Kück U
Lehrstuhl für Allgemeine und Molekulare Botanik, Ruhr-Universität, Bochum, Germany.
Mol Gen Genet. 2000 Mar;263(2):292-301. doi: 10.1007/s004380051171.
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.
交配型位点控制丝状子囊菌的交配和有性发育。在异宗配合的子囊菌粗糙脉孢菌中，赋予交配行为的基因在mat a和mat A交配型中由不同的DNA序列（特异型）组成。在同宗配合的真菌大孢粪壳菌中，与两种特异型对应的序列连续位于交配型位点中，该位点包含一个嵌合基因Smt A-3，其包含与在粗糙脉孢菌的mat A和mat a交配型特异型中发现的序列相似的序列。在本研究中，我们描述了大孢粪壳菌嵌合交配型区域和粗糙脉孢菌mat a特异型相应区域的比较转录分析。通过逆转录聚合酶链反应（RT-PCR）实验，我们在两种子囊菌的交配型位点中鉴定出了新的间隔序列，因此得出结论，在粗糙脉孢菌的mat a特异型中存在一个额外的开放阅读框（ORF），编码一个79个氨基酸的假定多肽。此外，我们的分析揭示了该新基因与粗糙脉孢菌中的mat a-1基因共转录。在大孢粪壳菌相应的交配型区域也发现了相同的转录模式，其中嵌合的Smt A-3基因与mat a特异的Smt a-1基因共转录。对Smt A-3 cDNA的分析揭示了两个内含子的选择性剪接。我们认为这是丝状真菌中蛋白质编码核基因共转录的首次报道。文中还讨论了新的开放阅读框在调节交配型基因表达中的可能功能。
