EXPRESSION OF CMS-UNIQUE AND FLANKING MITOCHONDRIAL-DNA SEQUENCES IN PHASEOLUS-VULGARIS L

The expression of mitochondrial DNA sequences unique to a cytoplasmica lly male-sterile (CMS) line of Phaseolus vulgaris was investigated. RN A-blot hybridizations with strand-specific probes demonstrated CMS-uni que transcripts (7.0, 6.8, 4.7, 3.3 and 2.8 kb) to be in the sense ori entation with respect to the longest open reading frames within the CM S-unique region. Hybridizations revealed co-transcription of CMS-uniqu e and upstream, atpA-coding sequences to generate the 6.8-kb RNA. Howe ver, hybridizations with CMS-unique and flanking DNA probes accounted for only 4.9 kb of the longest and most abundant (7.0 kb) CMS-unique t ranscript, providing indirect evidence for the involvement of a splici ng process in the generation of this transcript. Sedimentation experim ents demonstrated the association of 7.0- and 6.8-kb CMS-unique transc ripts with polyribosomes in seedlings and floral buds of a CMS line an d a line restored to fertility by the nuclear gene Fr2. However, stead y-state levels of the 7.0- and 6.8-kb transcripts were decreased in th e restored line relative to the CMS line.