Okamura Kohji, Wei John, Scherer Stephen W
The Centre for Applied Genomics, Program in Genetics and Genome Biology, The Hospital for Sick Children, MaRS Centre, Toronto, Ontario, Canada.
BMC Genomics. 2007 Jun 11;8:160. doi: 10.1186/1471-2164-8-160.
Chargaff's rule of DNA base composition, stating that DNA comprises equal amounts of adenine and thymine (%A = %T) and of guanine and cytosine (%C = %G), is well known because it was fundamental to the conception of the Watson-Crick model of DNA structure. His second parity rule stating that the base proportions of double-stranded DNA are also reflected in single-stranded DNA (%A = %T, %C = %G) is more obscure, likely because its biological basis and significance are still unresolved. Within each strand, the symmetry of single nucleotide composition extends even further, being demonstrated in the balance of di-, tri-, and multi-nucleotides with their respective complementary oligonucleotides.
Here, we propose that inversions are sufficient to account for the symmetry within each single-stranded DNA. Human mitochondrial DNA does not demonstrate such intra-strand parity, and we consider how its different functional drivers may relate to our theory. This concept is supported by the recent observation that inversions occur frequently.
Along with chromosomal duplications, inversions must have been shaping the architecture of genomes since the origin of life.
查加夫关于DNA碱基组成的规则指出，DNA中腺嘌呤和胸腺嘧啶的含量相等（%A = %T），鸟嘌呤和胞嘧啶的含量相等（%C = %G），这是众所周知的，因为它是沃森-克里克DNA结构模型概念的基础。他的第二条奇偶性规则指出，双链DNA的碱基比例也反映在单链DNA中（%A = %T，%C = %G），这一点更为晦涩难懂，可能是因为其生物学基础和意义仍未得到解决。在每条链内，单核苷酸组成的对称性进一步延伸，体现在二核苷酸、三核苷酸和多核苷酸与其各自互补寡核苷酸的平衡中。
在这里，我们提出倒位足以解释每条单链DNA内的对称性。人类线粒体DNA并未表现出这种链内奇偶性，我们思考了其不同的功能驱动因素可能与我们的理论有何关联。这一概念得到了最近关于倒位频繁发生这一观察结果的支持。
自生命起源以来，倒位与染色体复制一起，必定一直在塑造基因组的结构。
