Cold-sensitive of heterokaryons of Candida albicans.

Heterokaryons (hets) of Candida albicans are formed by fusing protoplasts of complementing auxotrophs. Het clones typically contain two kinds of monokaryons--parental-type auxotrophs arising by segregation of constituent nuclei, and prototrophs resulting from segregation of hybred nuclei formed through infrequent karyogamy within het cells. Hets, but not their parental strains or monokaryotic derivatives, die in cultures held at 5 degrees C-15 degrees C. Death occurs at a high exponential rate during the first two days at low temperature and at a lesser exponential rate thereafter: death rates are highest at 10 degrees C. Inactivation is not influenced significantly by the kinds of auxotrophies forcing heterokaryosis or by difference or identity in the wild type backgrounds of the auxotrophs used to construct the hets. It is also unaffected by amino acid analogues, specific inhibitors of mitochondrial protein synthesis or the general inhibitor of DNA synthesis, hydroxyurea. Inactivation is promoted by purine or pyrimidine analogues and impeded by specific inhibitors of mitochondrial DNA synthesis and transcription or oxidative phosphorylation. As a rule, cold-sensitive mutants of eukaryotic microorganisms are defective for production and assembly of components of cytoplasmic or mitochondrial ribosomes at restrictive temperatures. Our observations suggest that comparable defects in biogenesis of mitochondrial ribosomes are normal properties of C. albicans hets.