Borst P, Fase-Fowler F, Gibson W C
Mol Biochem Parasitol. 1987 Feb;23(1):31-8. doi: 10.1016/0166-6851(87)90184-8.
We show here that the kinetoplast DNA (kDNA) networks from six Trypanosoma evansi strains differ from those of T. brucei by their lack of maxi-circles and absence of mini-circle sequence heterogeneity. The lack of maxi-circles is sufficient to account for the inability of T. evansi to multiply in tsetse flies, since this requires functional mitochondria containing maxi-circle gene products. Judged by restriction enzyme analysis, five of the six T. evansi strains contain mini-circles that differ less than 4% in sequence. This type A mini-circle is found in strains from East Africa, West Africa and South America. Another strain from East Africa contains a very different mini-circle (type B), which shows about the same degree of hybridization to type A mini-circles as to a mini-circle from T. brucei. We propose that the pronounced sequence heterogeneity of the mini-circles of T. brucei has arisen by recombination of strains that had diverged for long periods of time in reproductive isolation. We further propose that the homogeneous mini-circles of T. evansi (and T. equiperdum) reflect the inability of species to mate. This proposal implies that mini-circle heterogeneity indicates (infrequent) genetic exchange and that all kinetoplastid flagellates with heterogeneous mini-circles exchange DNA.
我们在此表明，六种伊氏锥虫菌株的动基体DNA（kDNA）网络与布氏锥虫的不同，其缺乏大圆环且不存在小圆环序列异质性。缺乏大圆环足以解释伊氏锥虫无法在采采蝇体内繁殖，因为这需要含有大圆环基因产物的功能性线粒体。通过限制性酶切分析判断，六种伊氏锥虫菌株中有五种含有序列差异小于4%的小圆环。这种A型小圆环存在于来自东非、西非和南美的菌株中。另一种来自东非的菌株含有一种非常不同的小圆环（B型），它与A型小圆环的杂交程度与与布氏锥虫的小圆环的杂交程度大致相同。我们提出，布氏锥虫小圆环明显的序列异质性是由在生殖隔离中长时间分化的菌株重组产生的。我们进一步提出，伊氏锥虫（和马媾疫锥虫）的同质小圆环反映了物种无法交配。这一观点意味着小圆环异质性表明（不常见的）基因交换，并且所有具有异质小圆环的动基体鞭毛虫都会交换DNA。
