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Current Genetics ISSN: 0172-8083 (printed version) Polycistronic transcription and editing of the mitochondrial small subunit (SSU) ribosomal RNA in Dictyostelium discoideumC. Barth, U. Greferath, M. Kotsifas, and P.R. Fisher* *Department of Microbiology, La Trobe University, Bundoora 3083, Melbourne, Australia
Abstract Northern analyses and reverse transcription-polymerase chain-reaction (RT-PCR) experiments were performed on total RNA of Dictyostelium discoideum. The mitochondrial genes encoding the small subunit ribosomal RNA (SSU), cytochrome b (CYTB) and subunit 3 of the NADH dehydrogenase (ND3) were found to be cotranscribed. Further post-transcriptional processing resulted in a dicistronic transcript for CYTB and ND3, and a monocistronic SSU transcript. Markedly higher steady state transcript levels were detected for the mature SSU ribosomal RNA. A comparison of the SSU cDNA sequence with the mitochondrial DNA sequence of the SSU gene revealed C-to-U substitutional editing of the SSU ribosomal RNA at a single site, as a consequence of which the cDNA contained a PvuII site not present in the genomic DNA. The editing was shown to be highly efficient and to occur in the primary transcript before the release of the mature mRNA, rRNA and tRNAs. It is suggested that the editing may be required for normal pseudoknot formation in the 530 loop of the RNA and thus important for efficient, accurate translation in the mitochondria. Key words: Mitochondria. Ribosomal RNA. RNA editing. Polycistronic transcription. Received: 23 November 1998 / 1 March 1999 This research was supported by grants from the Australian Research Council. Communicated by: A. Brennicke
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