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

一些白念珠菌菌株比正常二倍体状态的其他菌株产生更高倍性的细胞群体比例。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了倍性漂移。从白念珠菌CBS5736的Arg4衍生物STN14和正常生长的STN22(arg4，pld^+)中分离到PLD-STN21(arg4，pld^-)，经紫外光照射后，从半分割菌落的弱生长段分离到PLD-STN21(arg4，pld^-)。STN22及其前体CBS5736在体外培养时菌落大小均一，但STN21在YPD平板上的菌落大小在培养初期表现出明显的不均一性，可观察到小菌落和大菌落两种类型的菌落。在STN21的另一种培养中，出现了一条染色体外带，其大小大于7号染色体，并丢失了7号染色体的两条带中的一条。Southern杂交实验表明，在染色体外带上存在SfiI片段7F，这是7号染色体的中心部分，但没有末端SfiI片段7C。原生质体融合实验表明，PLD至少有两个互补基团，其功能可能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.