RESTRICTED MITOCHONDRIAL DNA FRAGMENTS AS GENETIC MARKERS IN CYTOPLASMIC HYBRIDS

Abstract

ABSTRACT Cytoplasmic hybrids (cybrids) were made by fusing the chloramphenicol resistant (CAP-r) cytoplast of one mouse species with the chloramphenicol sensitive (CAP-s) whole cell of another mouse species or subspecies. The mitochondrial DNA (mt-DNA) of parents and cybrids was analysed by restriction endonuclease digestion and electrophoresis. Two types of cybrids were found: 1) those that maintained a balanced combination of endogenous, CAP-s and alien, CAP-r mt-DNA, and 2) those that showed repopulation by the alien CAP-r mt-DNA. When cybrids of the first type were returned to medium without CAP, the CAP-r phenotype segregated concordantly with the mt-DNA of the CAP-r subspecies, indicating that they are linked. In cybrids that showed repopulation, no segregation was observed, indicating that substitution was probably complete. No evidence of recombination was found. The repopulated heterospecific cybrids may be useful in determining which polypeptides are encoded by the mt-DNA. When CAP-s cells were treated with purified mt-DNA from CAP-r strains, CAP-s cells were efficiently “transformed” to CAP-r. Only the endogenous CAP-s mt-DNA was detected in these transformants. Fine structure restriction analysis suggests that small regions of the CAP-s mt-DNA may be altered, perhaps by incorporation of some CAP-r mt-DNA.