DNA synthesis in purified maize mitochondria.

We have developed an in organelle DNA synthesis system using isolated mitochondria from maize. The organelles used in this assay are shown to be intact by a number of criteria. Both the high molecular weight components and the smaller plasmid-like components of the mitochondrial genome are used as templates; however, the plasmid-like elements are relatively more active as templates. The termini of the linear plasmids--S-1, S-2 and the 2.3 kbp plasmids--are more highly labelled than internal regions, probably as a result of filling in of gaps at the termini mediated by a DNA polymerase or to exonuclease degradation of the 3' OH termini, with subsequent filling in. Although most of the DNA synthesis observed in this system most likely results from this type of synthesis at DNA nicks or termini, a small amount of specific, potentially replication-associated, synthesis is also detected.