DNA sequence analysis 3' to the Petunia S-pcf coding region has resulted in the identification of an open reading frame similar to mammalian mitochondrial genes for subunit 3 of the NADH dehydrogenase complex (nad3). Both the abnormal fused gene S-pcf and S-nad3 fall within the mitochondrial DNA region previously shown to be associated with cytoplasmic male sterility (CMS). The S-nad3 sequence, co-transcribed with S-pcf, is present in only one copy within the Petunia CMS genome. A homologous transcribed sequence from the mitochondrial genome of a fertile Petunia line has been identified. The coding region of the two genes are identical and they share homology for at least 800 bp downstream. The genes diverge 117 bp upstream of the nad3 start codon. Transcripts of the S-pcf/S-nad3 transcripts are similar in tissues of a fertility-restored line and a CMS line.