Transcripts of the Petunia mitochondrial cytoplasmic male sterility (CMS)-associated S-Pcf locus, which consists of three co-transcribed genes (pcf, NADH dehydrogenase subunit 3, and ribosomal protein S12), have been characterized in reproductive tissues of CMS and fertility restored (Rf) Petunia lines by nuclease protection experiments and by RNA blot hybridization. Three 5' transcript termini have been previously described. Two 3' transcript termini and an additional S-Pcf locus transcript have now been identified. The relative abundance of the three 5' transcript termini is influenced by the presence of the nuclear Rf gene. A decrease in the abundance of the -121 5' transcript terminus relative to the -266 and -522 termini is consistently seen in Petunia lines which are restored to fertility by the Rf gene, compared to CMS Petunia lines. An additional transcript with a 5' terminus within the urf-s region of pcf is much more abundant in immature bud and anther tissue than in leaf or suspension cells. The total abundance of pcf transcripts varies greatly between plants of different nuclear backgrounds which lack the nuclear Rf allele, indicating that other nuclear genes also influence expression of the S-Pcf locus.