Godelle B, Cartier D, Marie D, Brown S C, Siljak-Yakovlev S
Laboratoire d'Ecologie et Systématique Végétales, CNRS URA, Université Paris-Sud, Orsay, France.
Cytometry. 1993;14(6):618-26. doi: 10.1002/cyto.990140606.
A novel procedure for calculating base-pair frequencies in whole genomes is reported. This has been developed during a study of the role of heterochromatin in microevolution. Closely related species of the Crepis praemorsa complex have similar karyotypes but for their heterochromatin. The changes in relative AT frequency between species have been attributed to heterochromatin sequences by in situ banding of chromosomes with two base-specific fluorochromes. The absolute genome size of species, measured by cytofluorometry, correlated positively with increased karyotypic heterochromatin, as did the proportion of AT bases in the DNA. However, the determination of base content has called for a curvilinear interpretation of data obtained with two base-specific fluorochromes (bisbenzimide Hoechst 33342 and mithramycin), in contrast to the commonly assumed but erroneous direct relationship between fluorescence intensity and base content. Essentially, the fluorochromes' requirements for a sequence of certain base-pairs lead to the notion of Coefficients of Overspecificity: the result is a simple formula for calculating the AT proportion in a genome relative to a reference species from cytometric data, taking account of ligand binding statistics. These statistics and probabilities of oligonucleotide binding are essentially the same.
报道了一种计算全基因组碱基对频率的新方法。这是在研究异染色质在微观进化中的作用时开发的。皱叶酸模复合体的近缘物种具有相似的核型，但异染色质不同。通过用两种碱基特异性荧光染料对染色体进行原位显带，物种间相对AT频率的变化已归因于异染色质序列。通过细胞荧光测定法测量的物种绝对基因组大小与核型异染色质的增加呈正相关，DNA中AT碱基的比例也是如此。然而，与通常假设但错误的荧光强度与碱基含量之间的直接关系相反，碱基含量的测定需要对用两种碱基特异性荧光染料（双苯甲酰胺Hoechst 33342和光神霉素）获得的数据进行曲线解释。本质上，荧光染料对特定碱基对序列的要求导致了超特异性系数的概念：结果是一个简单的公式，用于根据细胞测量数据计算相对于参考物种的基因组中AT比例，同时考虑配体结合统计数据。这些统计数据和寡核苷酸结合的概率基本相同。
