Two plasmid-like DNAs, B2 and B3, were isolated from mitochondria of the cytoplasmic malesterile rice, A-58 CMS. Molecular clones having their complete sequences were constructed and used as probes of mitochondrial and nuclear genomes by Southern hybridization. No evidence was found that integrated copies of either one exist in the main mitochondrial genome, but sequences homologous to both were present in the nuclear genome. The complete nucleotide sequences of B2 and B3 were established and compared to those of rice B1 and B4 and to the 1.9-and the 1.4-kbp plasmid-like DNAs of maize. Many of the sequences were common to both plant species. © 1989 Springer-Verlag.