Probable synchronous replication of mitochondrial DNA in cultures of chick embryo fibroblasts.

Cultures of chick embryo fibroblasts were synchronized using a procedure previously described. The profile of incorporation of tritiated thymidine showed a main peak of nuclear DNA replication followed by a small peak between 18 and 24 hr after induction of the cell division, and representing 10 to 25% of the main peak. To identify this small peak, cells were treated with ethidium bromide(EB) chloramphenicol (CAP) or 9-B-D arabinofuranosyl adenine (Ara-A). When EB (1 mug ml-1) and CAP(25mug ml-1) were added at time of induction of mitosis (T0) or 14 hr later (T14) the small peak was suppressed whereas the main peak was not decreased. On the contrary, only the main peak was suppressed when Ara-A was added at T0 or T14. These results suggest that the peak might correspond to the synchronous replication of the mitochondrial DNA during the G2 and M phases of the cell division cycle.