GENETIC VARIABILITY OF THE YEAST CANIDA ALBICANS

致病酵母菌白色念珠菌表现出许多多态的例子。 变异，并自发产生高频率的突变体 不正常的群体。调查员此前证实， 殖民地形式的改变与频繁的单身和 多个大的染色体重排。并建议 正常菌株产生的自发染色体异常提供了一种 在这种无性微生物中遗传变异的手段。此外， 念珠菌属的近缘种和假丝酵母种内的菌株。 白念珠菌吸收某些选定碳源的能力各不相同。 进一步的测试显示，所有自发的形态突变 也极大地改变了碳和氮的同化模式 来源，包括增长能力的丧失和/或获得 媒体。最重要的是，突变体获得了同化 直接选择某些碳源，并将每种类型关联起来 它们的电泳性核型发生了特殊的变化。这个 研究人员已经确定了表型和电泳性核型 在10个Sor(利用山梨糖)和15个Ara(利用D-Arbinose)突变体中， 并发现他们由三个主要小组组成，通常得到 特定的染色体重排。尽管染色体的异常 可能是次要影响，可能不直接对 阳性突变表型的关联表明，每一类 阳性突变体可能是通过不同的遗传改变而形成的。这个 调查人员将检查Sor和Ara突变体是否通过选择产生 或通过在未分裂的细胞中进行适应性突变 对选择性条件的反应。延迟亮相和 突变菌落的积累表明，至少有一些突变可能是 由不分裂的细胞产生的。调查员提议克隆 负责Sor和Ara表型的基因或DNA片段，通过 正常品系的互补。此外，他还建议确定 亲本菌株与Sor和Ara突变体的DNA差异， 通过“代表性差异分析”(RDA)，一个基于 聚合酶链式反应扩增限制性内切酶片段及其竞争抑制 通过相似片段的扩增，这样只有变种 碎片最终会被找回。仅在SOR中发现的DNA序列 突变体，连同相关正常片段的DNA序列可能揭示 形成阳性突变体的过程。此外，他还建议 利用“差异显示”技术筛选优势表达基因 程序，这依赖于cDNA片段的聚合酶链式反应。三位一体 分子方法可能导致对突变的鉴定 基因的改变和差异激活(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.