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首页> 外文OA文献 >Variations in the number of ribosomal DNA units in morphological mutants and normal strains of Candida albicans and in normal strains of Saccharomyces cerevisiae.
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Variations in the number of ribosomal DNA units in morphological mutants and normal strains of Candida albicans and in normal strains of Saccharomyces cerevisiae.

机译：白色念珠菌的形态突变体和正常菌株以及酿酒酵母的正常菌株中核糖体DNA单元数目的变化。

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Naturally occurring strains of Candida albicans are opportunistic pathogens that lack a sexual cycle and that are usually diploids with eight pairs of chromosomes. C. albicans spontaneously gives rise to a high frequency of colonial morphology mutants with altered electrophoretic karyotypes, involving one or more of their chromosomes. However, the most frequent changes involve chromosome VIII, which contains the genes coding for ribosomal DNA (rDNA) units. We have used restriction fragment lengths to analyze the number and physical array of the rDNA units on chromosome VIII in four normal clinical strains and seven morphological mutants derived spontaneously from one of the clinical isolates. HindIII does not cleave the rDNA repeats and liberates the tandem rDNA cluster from each homolog of chromosome VIII as a single fragment, whereas the cleavage at a single site by NotI reveals the size of the single rDNA unit. All clinical strains and morphological mutants differed greatly in the number of rDNA units per cluster and per cell. The four clinical isolates differed additionally among themselves by the size of the single rDNA unit. For a total of 25 chromosome VIII homologs in a total of 11 strains considered, the variability of chromosome VIII was exclusively due to the length of rDNA clusters (or the number of rDNA units) in approximately 92% of the cases, whereas the others involved other rearrangements of chromosome VIII. Only slight variations in the number of rDNA units were observed among 10 random C. albicans subclones and 10 random Saccharomyces cerevisiae subclones grown for a prolonged time at 22 degrees C. However, when grown faster at optimal temperatures of 37 and 30 degrees C, respectively, both fungi accumulated higher numbers of rDNA units, suggesting that this condition is selected for in rapidly growing cells. The morphological mutants, in comparison with the C. albicans subclones, contained a markedly wider distribution of the number of rDNA units, suggesting that a distinct process may be involved in altering the number of rDNA units in these mutants.
机译：天然白色念珠菌菌株是机会性病原体，缺乏性周期，通常是具有八对染色体的二倍体。白色念珠菌自发地产生具有改变的电泳核型，涉及其一个或多个染色体的殖民地形态突变体的高频率。但是，最频繁的变化涉及第VIII号染色体，该染色体包含编码核糖体DNA（rDNA）单元的基因。我们已经使用限制酶切片段的长度来分析了四种正常临床菌株和自一种临床分离株自发衍生的七个形态突变体中VIII染色体上rDNA单元的数量和物理排列。 HindIII不会切割rDNA重复序列，并从VIII号染色体的每个同源物中释放出串联rDNA簇，成为一个片段，而NotI在一个位点的切割揭示了单个rDNA单元的大小。所有临床菌株和形态突变体在每个簇和每个细胞的rDNA单位数量上差异很大。四种临床分离株之间的差异还在于单个rDNA单元的大小。对于总共考虑的11个菌株中的总共25个VIII染色体同源物，VIII染色体的变异性仅是由于在大约92％的情况下rDNA簇的长度（或rDNA单位的数量）引起的，而其他情况涉及VIII染色体的其他重排。在10个随机的白色念珠菌亚克隆和10个随机的酿酒酵母亚克隆中，rDNA单元的数量仅观察到微小的变化，它们分别在22摄氏度下长时间生长。然而，当它们分别在37和30摄氏度的最佳温度下生长较快时， ，这两种真菌都积累了更高数量的rDNA单位，表明在快速生长的细胞中选择了这种条件。与白色念珠菌亚克隆相比，形态突变体包含明显更广泛的rDNA单元分布，这表明改变这些突变体中rDNA单元的数量可能涉及一个独特的过程。

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