Extrachromosomal inheritance inSchizosaccharomyces pombe

Summary Spontaneous chloramphenicol (cap^r)- and erythromycin (ery^r)-resistant mutants were isolated from strain ade7–50 h^- and the antimycin-resistant mutant ana^r-8 ade 7–50 h^- of Schizosaccharomyces pombe (Sch. p.). By mitotic segregation analysis all 154 cap^r- and 120 ery^r-mutants derived from ade 7–50 h^- proved to be recessive chromosomal, whereas all 108 cap^r- and 200 ery^r-mutants originating from ana^r-8 were extrachromosomally inherited. The rate of spontaneous cap^r- and ery^r-mutants was about hundredfold in ana^r-8 compared to ade 7–50 h^-. Growth of cap^r-and ery^r-mutants was not inhibited by chloramphenicol or erythromycin, respectively, in glucose-medium and only slightly in glycerol-medium at concentrations which completely inhibited ana^r-8. By mitotic segregation-, tetrad-, and mitotic haploidization-analysis the extrachromosomal inheritance of mutants derived from ana^r-8 was established. Segregational patterns of cap^r- and ery^r-determinats during mitosis, meiosis, and mitotic haplidization of diploids are discussed.