GENETIC VARIABILITY OF THE YEAST CANDIDA ALBICANS

致病酵母C.白色念珠菌表现出许多多态性 变异，并自发产生高频率的突变体， 异常菌落 研究人员先前确定， 殖民地形式的改变与频繁的单一和 多重染色体重排 并建议， 由正常菌株引起的自发染色体畸变提供了一种 在这种无性微生物中进行遗传变异的手段。 此外，委员会认为， 假丝酵母属的近缘种，以及假丝酵母属种内的菌株。 白色念珠菌同化某些选定碳源的能力不同。 进一步的测试表明，所有自发的形态突变体， 也改变了碳和氮的同化模式 来源，包括失去和/或获得在某些 媒体 最重要的是，变种人获得了同化的能力 直接选择一定的碳源，每种碳源都与 其电泳核型发生了特殊的变化。 的 研究者已经通过电泳核型分析确定了表型特征 10个Sor+（利用山梨糖）和15个Ara+（利用D-阿拉伯糖）突变体， 并发现他们包括三个主要群体， 特异性染色体重排 虽然染色体畸变 可能是次要影响，可能不直接负责 阳性突变体表型，该关联表明， 阳性突变体可能是由不同的遗传改变形成的。 的 研究者将检查Sor+和Ara+突变体是否通过选择产生 或通过在非分裂细胞中的适应性诱变， 对选择性条件的反应。 延迟出现和 突变菌落的积累表明，至少有一些突变体可能是 由不分裂的细胞产生。 研究人员建议克隆 负责Sor+和Ara+表型的基因或DNA片段， 正常菌株的互补。 此外，他建议确定 亲本菌株与Sor+和Ara+突变体之间的DNA差异， 通过"代表性差异分析"（RDA），一种基于 通过PCR扩增限制性片段， 通过相似片段的扩增，使得仅变体 碎片最终被回收。 仅在Sor+中发现的DNA序列 突变体，沿着与相关正常节段的DNA序列可以揭示 形成阳性突变体的过程。 此外，他建议 通过"差异显示"鉴定优先表达的基因 方法，其依赖于cDNA片段的PCR扩增。 三 分子方法可以鉴定出突变的 改变和基因差异激活（或沉默）， 阳性突变体

The pathogenic yeast c. albicans exhibits numerous examples of polymorphic variations, and spontaneously produces high frequencies of mutants having abnormal colonies. The investigator previously established that alterations of colonial forms are associated with frequent single and multiple gross chromosomal rearrangements. and has suggested that the spontaneous chromosomal aberrations arising from normal strains provide a means for genetic variation in this asexual microorganism. Furthermore, related species of the genus Candida, and strains within species of C. albicans vary in their ability to assimilate some selected carbon sources. Further tests revealed that all of the spontaneous morphological mutants also had invidiously altered assimilation patterns for carbon and nitrogen sources, including the loss and/or gain of ability to grow on certain media. Most importantly, mutants acquiring the ability to assimilate certain carbon sources were selected directly, and each type was associated with a specific change in their electrophoretic karyotypes. The investigator has characterized the phenotypes an electrophoretic karyotypes of 10 Sor+ (sorbose utilizes) and 15 Ara+ (D-arbinose utilizes) mutants, and found them to comprise three major groups generally assisted with specific chromosomal rearrangements. Although the chromosomal aberrations may be secondary effects, and may not be directly responsible for the positive mutant phenotypes, the association indicates that each class of positive mutants may have been formed by different genetic alteration. The investigator will examine if the Sor+ and Ara+ mutants arise by selection of preexisting mutants or by adaptative mutagenesis in nondividing cells in response to the selective condition. The delayed appearance and the accumulation of mutant colonies suggest that at least some mutants may be arising from nondividing cells. The investigator proposes to clone the genes or DNA segments responsible for the Sor+ and Ara+ phenotypes, by complementation of a normal strain. Also, he proposes to identify the differences of DNA between the parental strain and Sor+ and Ara+ mutants, by "representational difference analysis" (RDA), a procedure based on amplifying restriction fragments by PCR and the competitive inhibition of the amplification by similar fragments, such that only the variant fragments are ultimately recovered. DNA sequences found only in Sor+ mutants, along with DNA sequences of the related normal segments may reveal the process by which positive mutants are formed. In addition, he proposes to identify preferentially expressed genes by the "differential display" procedure, which relies on PCR amplification of cDNA fragments. The three molecular approaches could result in the identification of the mutational alterations and the genes differentially activated (or silenced) in the positive mutants.