Molecular and General Genetics 256: 661-673 (1997)

Transcripts at the mating type locus of Cochliobolus heterostrophus

Gerhard Leubner-Metzger, Benjamin A. Horwitz, Olen C. Yoder, B. Gillian Turgeon

Cornell University, Department of Plant Pathology, 334 Plant Science Bldg., Ithaca, NY 14853, USA Received: 1 March 1997 / Accepted: 21 June 1997

Abstract. The single mating type locus (MAT) of the heterothallic ascomycete Cochliobolus heterostrophus is composed of a pair of unlike sequences called idiomorphs that each encode one MAT-specific gene (MAT-1 and MAT-2). MAT transcripts were observed in blots of poly(A)+ RNA isolated from cultures grown in minimal medium, but were not detectable after growth of the fungus in complete medium, suggesting that transcription of MAT is tightly regulated. The idiomorphs (MAT-1 = 1297 bp, MAT-2 = 1171 bp) encode transcripts of 2.2 kb (MAT-1) and 2.1 kb (MAT-2) which start 5' and end 3' of the idiomorph in sequences common to both mating types. Analyses of MAT-1 and MAT-2 cDNAs revealed obligatory splicing of one intron (MAT-1 = 55 bp; MAT-2 = 52 bp) within each MAT-specific ORF and optional splicing of two introns (63 and 79 bp) in the long (approximately 0.55 kb) 5' untranslated leader sequences; the 3' untranslated region is 0.46 kb. Transcription start sites were found 5' of and within the 79 bp intron. Optional splicing of the upstream introns and at least two transcription start sites result in three types of transcript: Type I with both 5' introns spliced, Type II with only the 63 bp intron spliced, and Type III with neither 5' intron spliced. The three transcript types are distinguished by various combinations of four short ORFs encoded by the corresponding genomic DNA, in the leader sequences of the MAT message. Transcript structure suggests several mechanisms by which expression of the MAT genes might be regulated at the level of translation during sexual development. Key words: Ascomycete, Intron, uORF, UTR, mRNA leader

Article in PDF format (540 KB) Abstract          Fig. 1          Fig. 2          Fig. 3          Fig. 4 Introns            Fig. 5           Fig. 6          Fig. 7          Fig. 8

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