When homothallic cells of Schizosaccharomyces pombe were plated on agar sporulation medium, a few residual divisions were usually observed before induction of conjugation and sporulation. Four cells resulting from the last two residual divisions were usually lined; the "four-linedcell" formed. Each four-lined-cell contained only one zygote by sistercellor non-sistercell-copulation, and never two zygotes by two sistercellcopulations. Some of the remaining non-zygotic sistercells divided once again and resulted in the new formation of the four-lined-cell which contained only one zygote. The remaining non-zygotic cell of the fourlined-cell could conjugate with that of another four-lined-cell. These results suggest that the four-lined-cell is to be regarded as one unit with respect to zygote formation.Cells of Schizosaccharomyces pombe are usually haploid during vegetative growth. It is only when the culture medium becomes exhausted, particularly of nitrogen, that diploid zygotes are formed by pairwise cell fusion. If left undisturbed, these zygotes undergo meiosis and sporulation. In homothallic cells even the daughter cells resulting from a cell division (sistercells) can progress through this reproductive process (1). The mating type locus and its function were studied in the homothallic cells, and the "flip-flop" model was proposed (2), in which the frequency of mating-type switching was approximately random (3).When proliferating cells of S. pombe were plated on agar sporulation medium, a few residual divisions were usually observed before the induction of conjugation and sporulation (3). Proliferating cells elongated primarily at the end distal to the new fission scar which appeared at the cell plate during division (4). We observed that since after the final residual division cells did not elongate, four cells resulting from the last two residual divisions were usually lined; the "four-lined-
Cells of Schizosaccharomyces pombe grown in the presence of aculeacin A, a peptide antibiotic, were lysed resulting the death of cells. Under high osmolarity, the cellular lysis induced by aculeacin A was considerably reduced. The use of synchronous-culture systems distinguished cell elongation from cell division revealed that the sites of aculeacin A-induced lysis on the fission yeast were the end(s) and the cell plate region, corresponded to the regions of the cell wall synthesis. Aculeacin A-resistant survivors exhibited morphological alterations which were swollen at one or both ends of the cell and appeared drumstick or dumbbel like; the wall of the bulge region was observed to be stained with a fluorescent brightner, as well as that of the cell plate region. These effects of aculeacin A are discussed as compared with effects of 2-deoxy-D-glucose.
Cells of the fission yeast Schizosaccharomyces pombe, normally sausage-shaped, changed to a round-bottomed flask (RBF)-like morphology during growth in the presence of aculeacin A (Acu), an antifungal antibiotic. The volume of RBF-like cells was comparable to that of the control cells. After being transferred to normal conditions (without Acu at 25 "C), the RBF-like cells continued to grow at the cylindrical and/or spherical end(s) and then the septum at the subsequent division of the cells was formed without exception at the boundary plane between the spheroidal and the cylindrical region; it is at this boundary that the nucleus was located before mitosis. Hence the RBF-like cell divided into a spheroidal and a cylindrical sib at the first cell division. At the end of the second cell cycle, the spheroidal and the cylindrical progeny divided into two spheroidal and two cylindrical sibs respectively. The values of the mean length (long/short) and volume (biglsmall) ratios of paired sibs were larger in order of (a) cylindrical normal, with both mean ratios 1.06; (b) cylindrical control; (c) cylindrical progeny of RBF-like cell; (d) spheroidal progeny of RBF-like cell; and (e) RBF-like cell, whose mean length ratio was 1.25 but whose mean volume ratio was 1.94. That is, the more the morphology deviated from the cylindrical form, the greater was the degree of asymmetry. There was no rule relating the biases to the growth pole in these asymmetries.
~~~ ~~ t Offprint requests should be sent to the Ottawa address.Ahhrc~riutions: Acu, aculeacin A ; RBF-like, round-bottomed flask-like.0001-2795 0 1986 Government of Canada
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