The human fungal pathogen Candida albicans displays a very high degree of plasticity, including the types of genomic changes frequently observed with cancer cells, such as gross chromosomal rearrangements, aneuploidy, and loss of heterozygosity. Despite its relevance to every aspect of genetics and evolution of this pathogen, our understanding of the mutation process and its bearing on organismal fitness remains quite limited. Here, we have evaluated and compared two approaches to estimate the mutation frequency at three ORFs/regions (HIS4, CEN4 and EST2) of the C. albicans genome. Sequencing of individual DNA molecules (clone-by-clone sequencing) identified de novo mutations at these DNA regions, whose frequency was similar to that observed for S. cerevisiae at homolog sites following the same approach. However, mutations were not detected when the same regions were directly sequenced from the pooled DNA. In addition, in the absence of the homologous recombination protein Rad52, mutation frequency within these sites remained unaltered. The use of an alternative polymerase also found mutations. These results suggest that at least some mutations are artifacts caused by the polymerase used, advising that post-PCR procedures might generate mutations which may become undistinguishable from the genuine mutations and thus may interfere with mutational analysis. Furthermore, we recommend that new mutations found in the sequences of cloned alleles used for the determination of haplotypes should be contrasted with the sequence yielded by the pooled DNA.

译文

:人类真菌病原体白色念珠菌具有很高的可塑性,包括癌细胞经常观察到的基因组变化类型,例如总体染色体重排,非整倍性和杂合性丧失。尽管它与这种病原体的遗传学和进化的各个方面都相关,但我们对突变过程及其对机体适应性的了解仍然十分有限。在这里,我们评估和比较了两种方法来估计白色念珠菌基因组的三个ORF /区域(HIS4,CEN4和EST2)的突变频率。单个DNA分子的测序(逐个克隆测序)在这些DNA区域识别出从头突变,其频率与酿酒酵母在同源位点处观察到的频率相似。但是,当从合并的DNA直接对相同区域进行测序时,未检测到突变。另外,在缺少同源重组蛋白Rad52的情况下,这些位点内的突变频率保持不变。使用替代的聚合酶也发现了突变。这些结果表明,至少某些突变是由使用的聚合酶引起的伪像,建议PCR后操作可能会产生突变,这些突变可能与真正的突变无法区分开,因此可能会干扰突变分析。此外,我们建议将用于确定单倍型的克隆等位基因序列中发现的新突变与汇集的DNA产生的序列进行对比。

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