High Frequency Chromosome Rearrangement and Variation of Cell Morphology in The Yeast Candida Albicans.

紫外线照射处理的无性酵母白色念珠菌，以及热带念珠菌，引起形态突变，表现出异常菌落。这些群体突变的发生频率为10^<-2>至10^<-3>，这些现象被称为遗传不稳定。脉冲场凝胶电泳（PFGE）显示了染色体大小DNA的不同带型，表明染色体重排的发生与遗传不稳定性有关。这些突变株对每种菌落产生特定类型的细胞。此外，在这些突变菌落中还发现了具有多倍体状态的大细胞。为了明确多倍体细胞的发生与遗传不稳定性之间的关系，我们分离了一株白色念珠菌菌株，#31-30，在高温（37℃）下培养，产生了多倍体细胞。该突变体染色在高温下孵育，产生各种形态突变体和高频营养缺陷突变体。这些营养不良的生命体是由原先存在的杂合状态转变为纯合状态而产生的。在低温（28℃）下，几乎没有多倍体细胞出现，也没有突变菌落产生。通过原生质体融合，这种突变表型能够转移到其他菌株的白色念珠菌。有着不同的遗传背景。37次处理后得到的多倍体细胞经ficoll -密度梯度离心分离并镀成菌落。在这些菌落中，营养不良菌落和菌落形态变异占20%以上。杂交实验表明，在遗传不稳定突变株中，一些不同模式的染色体DNA条带存在RDNA重复序列。在原生质体融合的情况下，发现在融合过程中发生染色体排列，并检测到两种重复序列，其中一种是RDNA，另一种有待鉴定。

UV irradiation treatment of the asexual yeast Candida albicans, as well as C. tropicalis, gave rise to morphological mutants exhibiting abnormal colonies. The frequency of occurrence of these colony mutants was 10^<-2> to 10^<-3> and these phenomena were termed as genetic instability. Pulsed-field gel electrophoresis (PFGE) showed different banding pattern of chromosome-sized DNA, suggesting the occurrence of chromosonal rearrangements associated with genetic instability. These mutant strains produced cells of specific type to each type of colony. Furthermore, large cells with polyploid states were also found among these mutant colonies.In order to clarify relation between the occurrence of polyploid cells and genetic instability, a variant of C. albicans strain, #31-30, was isolated, which produced polyploid cells when incubated at high temperature (37ﾟC). Incubation of this mutant stain at high temperature gave various morphological mutants and auxotrophic mutants at high frequency. These auxotrophic ones were produced as outaion previously existing heterozygous state to be homozygous oife. At low temperature (28ﾟC), scarecely any polyploid cells appeared, nor mutant colonies were produced. By protoplast fusion, this mutant phenotype was capable of being transferred to the other strains of C. albicans. with different genetic backgrounds.Polyploid cells, which appeared after 37ﾟC-treatment, were fractionated by Ficoll-density gradient centrifugalization and plated to colonies. Among these colonies, auxotrophic ones as well as colony-morphology variants accounted for more than 20%. Hybridization experiments showed that some of the different patterns of chromosomal DNA bands among the mutant strains with genetic instability had RDNA repeats.In the case of protoplast fusion, chromosome arramgement was found to occur during fusion process and two types of repeated sequences were detected, one of which was RDNA but the other remained to be identified.