Co-transcription of orf25 and coxIII in rice mitochondria.

Southern hybridization analysis using homologous maize probes indicated that orf25 and coxIII are closely linked in the mitochondrial genome of rice (Oryza sativa) cultivar IR36. The two coding regions were found on the same 5.1 kb BamHI fragment, and this fragment was cloned, mapped and partially sequenced. Using probes for each gene derived from the rice clone, a 2.4 kb dicistronic mRNA transcript was found containing both orf25 and coxIII coding regions. Multiple 5' ends were identified by primer extension analysis and a double stem/loop structure was mapped to the 3' end. The orf25 coding region shares greater than 85% identity with orf25 sequences from maize, tobacco and wheat, suggesting that orf25 may code for a conserved protein product.