MOLECULAR MECHANISM OF PLOIDY-SHIFT AND VARIATION OF COLONY MORPHOLOGY IN THE IMPERFECT YEASTS

白念珠菌的某些菌株产生的细胞群体的比例具有比正常二倍体状态下的其它菌株更高的倍性。作者将该表型命名为Pld^-。在两种不同的倍性状态之间观察到倍性移位。在用白色念珠菌CBS 5736的arg 4衍生物STN 14进行UV照射后，从半扇形菌落的弱生长扇形中分离出Pld-STN 21（arg 4，Pld^-），并从另一正常生长扇形中分离出STN 22（arg 4，Pld^+）。当铺板时，STN 22以及其祖细胞CBS 5736显示出菌落大小，但STN 21在孵育的早期阶段在YPD平板上显示出菌落大小的特征性异质性：用PFGE技术分离出菌株的染色体，STN 21的部分培养物显示7号染色体的单带，提示由于染色体不分离的发生。另一种培养物STN 21产生了一条染色体外带，其大小大于7号染色体，并且7号染色体的两条带中的一条丢失。Southern杂交结果表明，在7号染色体的中部有一个SfiI片段7 F存在于染色体外带，而没有SfiI片段7 C的末端。原生质体融合实验表明，PLD至少有两个互补群，其功能可以稳定倍性状态和染色体保真度。

Some strains of Candida albicans poroduce a proportion of the cell population with a higher ploidy than the rest in normal diploid state. This phenotype was named as Pld^-by the author. Ploidy-shift was observed between two different ploidy states. Pld-STN21 (arg4, Pld^-) was isolated from a weakly growing sector of a half-sectored colony, after UV-irradiation of STN14, an arg4 derivative of C.albicans CBS5736 and from the other normally growing sector, STN22 (arg4, Pld^+) was isolated. STN22, as well as its progenitor, CBS5736, showed a homogeneus colony size when plated out, but STN21 showed a characteristic heterogeneity of colony size on YPD plates at an early stage of incubation : two types of colonies, small ones and large ones, were observed.The chromosomes of these strains were separated out by PFGE.Some culture of STN21 showed the single band of chromosome 7, suggesting due to the occurrence of chromosome non-disjunction. The other culture of STN21 gave an extrachromosomal band, the size of which was larger than that of chromosome 7, and the loss of one of the two bands of chromosome 7. Southern blot hybridization experiments showed the existence of a SfiI fragment 7F,a central portion of chromosome 7, on the extrachromosomal band but the absence of a terminal SfiI fragment 7C.Protoplast fusion experiments showed, at least, two complementation groups of PLD,the function of which may stabilize both ploidy state and chromosome fidelity.