Unique features of the mitochondrial rolling circle-plasmid mp1 from the higher plant Chenopodium album (L.).

摘要

The structure and replication of the mitochondrial circular DNA plasmid mp1 (1309 bp) from C. album was analysed. Two-dimensional gel electrophoresis (2DE) revealed the existence of oligomers of up to a decamer in addition to the prevailing monomeric form. The migration behaviour of cut replication intermediates during 2DE was consistent with a rolling circle (RC) type of replication. Entirely single-stranded plasmid copies hybridizing only with one of the two DNA strands were identified, indicating the existence of an asymmetric RC replication mechanism. mp1 has, with respect to its replication, some unique features compared with bacterial RC plasmids. A strand-specific nicking site (origin of RC replication) was localized on the plasmid by primer extension studies. Nicks in the plasmid were found to occur at any one of six nucleotides (TAAG/GG) around position 735 of the leading strand. This sequence showed no homology to origin motifs from known bacterial RC replicons. mp1 is the first described RC plasmid in a higher plant. Nucleotide sequence data have been submitted to the EMBL/GenBank/DDBJ databases under the accession number X58911.