Linear, extrachromosomal DNA's of the filamentous fungus Ascobolus immersus are localized within the mitochondria. These linear plasmids have no homology to the high molecular weight mtDNA (hmw mtDNA). For analysis of plasmid replication an in organello DNA synthesis system was developed, in which radionucleotides were incorporated into intact mitochondria. Plasmid DNA is labelled preferentially in this system. From replication analysis of a specific plasmid there is evidence of a virus-like protein-primed replication. Sequence analysis of this plasmid reveals that a viral DNA polymerase is encoded. Thus, these genetic elements presumably are viral remnants rather than true plasmids.

In organello replication and viral affinity of linear, extrachromosomal DNA of the ascomycete Ascobolus immersus

Cultured cells of Glycine max (L.) Merr. v. Corsoy were permeabilized by treatment with L-α-lysophosphatidylcholine (LPC). The permeabilized cells were capable of uptake and incorporation of deoxynucleoside triphosphates into DNA. Incorporation of exogenous nucleotides into DNA was linear for at least 90 minutes and the initial rate of incorporation approached 50% of the theoretical in vivo rate of DNA synthesis. However, DNA synthesis in the permeabilized cells was unaffected by the potent DNA polymerase α inhibitor, aphidicolin. Analysis of newly synthesized DNA by molecular hybridization revealed that only organellar DNA was synthesized by the permeabilized cells. The LPC treated cells were also permeable to a protein as large as DNase I. The permeabilized cells were capable of RNA and protein synthesis as indicated by incorporation of radiolabeled UTP and leucine, respectively, into acid-precipitable material.

Organellar DNA synthesis in permeabilized soybean cells.

Isolated chloroplasts are capable of synthesizing chloroplast DNA in the presence of Mg2+ and deoxynucleoside triphosphates. The in vitro reaction proceeds for at least 60 min and is inhibited by KCl and N-ethylmaleimide. Stretches of several hundred nucleotides in length are synthesized within an hour. Little or no inhibition is shown by aphidicolin (an inhibitor of eukaryotic DNA polymerase a), dideoxythymidine triphosphate (an inhibitor of eukaryotic DNA polymerases P and y), nalidixic acid, or rifampicin. Ethidium bromide is a moderate inhibitor of DNA synthesis in the isolated chloro- Eukaryotic cells are characterized by compartmentalization of those cellular components which contain their own genetic apparatus. In animal cells, the nuclear compartment has a genomic organization and DNA replication machinery which is apparently quite different from that in the other cellular compartment, the mitochondria (Kasamatsu et al., 1974). Higher plant cells contain three, rather than two, cellular compartments (Olson, 198 1) since they contain another au-

https://epub.ub.uni-muenchen.de/5372/1/Zimmermann_Wolfgang_5372.pdf

M. Zama

Papers

Deoxyribonucleic Acid Synthesis in Isolated Chloroplasts and Chloroplast Extracts of Maize