Various cytoplasms of broad bean contain three mitochondrial plasmids (mtp1, 2 and 3), previously described. In cytoplasm 350 we have observed several additional mitochondrial plasmids, varying in number and in identity according to the nuclear background. Replacement of the nucleus by backcrossing led to the appearance or disappearance of additional plasmids, indicating that the nuclear genome controls either the creation or the copy level of mitochondrial plasmids. Analysis of eight variant additional plasmids (mtp4-11) suggests that they all result from a double recombination event between mtp1 and mtp2. In all cases, one recombination point was located within a 276-bp sequence, identical in both plasmids. For 7 plasmids, the region in which the second recombination event occurred could be narrowed down to a short stretch containing imperfect tandem repeats of a 31-bp motif. The largest sequence shared by the recombination regions was hexanucleotide GCGACG.
Three mitochondrial plasmids (1704, 1695 and 1478 bp) were isolated from sterile cytoplasms of Vicia faba L. and cloned into a bacterial plasmid vector. Their nucleotide sequence was found to be 99 to 100% homologous to their counterparts isolated from a fertile cytoplasm (J.A. Wahleithner and D.R. Wolstenholme, Curr Genet 12 (1987) 55-76). Several overlapping transcripts were localized in the region which is unique to each of the three plasmids. S1 nuclease mapping indicated for all of them several 3' termini but a unique 5' boundary which was located downstream of the consensus sequence CNTAAGTGANNNNNGAA also found at the transcript 5' boundary of other plant mitochondrial plasmids. Southern blot hybridization with nuclear DNA indicated the presence of nuclear sequences homologous to each plasmid.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.