2.0kb Hind III fragment isolated from cytoplasmic male-sterile carrot mitochondria, designated PKT5, was hybridized to ORF13 which is the coding region of a unique polypeptide in maize CMS (Dewey et al., 1986). Sequence analysis indicated that PKT5 is consisted of 3 domains. Domain 1 was identical to the 5'-flanking region of atp6 in maize CMS-TURF2H3 sequence (Dewey et al., 1986). Domain 2 contained a novel ORF encoding 72 amino acids, which was extremely homologous to the amino-terminal 67 amino acids of the unique ORF13 in maize CMS. Domain 3 except an amino acid change (Ile⁸⁷=ATT for Asn⁸⁷=AAT), was identical to ORF25 polypeptide in maize CMS. Connective sequences of these 3 domains were also highly homologous to the maize CMS-TURF2H3 sequence. Out of 7 recombination points in maize CMS-TURF2H3 sequence, at least 4 points were conserved in PKT5 sequence.