INTERSTRAIN TRANSFER OF THE 2μm DNA PLASMID OFSACCHAROMYCESBY CYTODUCTION

Respiratory-sufficient, [rho+], cytoductants were obtained from matings where the respiratory-deficient, [rho−], parent lacked 2μm DNA. In these crosses, the cytoduction frequency (no. cytoductants × 100/no. cytoductants plus no. diploids) was ca. 20% or less, even though the [rho+] parent was defective in nuclear fusion. This apparent suppression of the kar defect was specific to matings where the kar nucleus was derived from a [rho+] cytoplasm, but was not a consequence of the lack of 2μm DNA in the recipient strains. Of 16 cytoductants examined from such a cross, only 3 contained 2μm DNA. This confirmed an anomalous mode of cytoplasmic inheritance for the plasmid but demonstrated that the frequency of transmission during cytoduction can be somewhat lower than has been reported previously. The plasmid, in those [cir+] cytoductants which received it, was stably maintained over more than 120 cell doublings. From a preliminary comparison of [cir+] and [ciro] cytoductants, no evidence for a plasmid-specific phenotype was obtained.