Complex organization of the soybean mitochondrial genome: recombination repeats and multiple transcripts at the atpA loci
1993
Chanut, F.A. (Utah Univ. (USA). Howard Hughes Medical Inst. Eccles Inst. of Human Genetics) | Grabau, E.A. | Gesteland, R.F.
Identification of the soybean mitochondrial atpA open reading frame (atpA ORF) was based on sequence similarity with atpA genes in other plant mitochondria and partial protein sequencing. The atpA reading frame ends with 4 tandem UGA codons which overlap 4 tandem AUG codons initiating an unidentified reading frame, orf214. The atpA-orf214 region is found in multiple sequence contexts in soybean mitochondrial DNA (mtDNA), which can be attributed to the presence of 2 recombination repeats. A 1-kb repeat spans 600 nucleotides (nt) of atpA N-terminal coding region and 400 nt of upstream sequence. Its four configurations correspond to 2 full- length atpA-orf214 genes and 2 truncated pseudogenes. A 2-kb repeat lies 3 kb downstream from the 1-kb repeat. Restriction maps of cosmid clones suggest that a 10-kb segment containing both repeats is itself duplicated in the mt genome. With 2 recombination repeats present in a total of 3 copies per genome, soybean mtDNA is expected to consist of a complex population of subgenomic molecules. Transcription of the atpA loci was analysed by Northern blotting and S1 nuclease protection. The atpA genes express multiple transcripts with one major 3'end and heterogeneous 5'sequences extending several kb upstream of the atpA coding region. The atpA gene and orf214 are co-transcribed on all major transcripts. The pseudogenes do not express stable RNAs.
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