Sommerville J, Scheer U
Chromosoma. 1982;86(1):95-113. doi: 10.1007/BF00330732.
Repeat sequences are transcribed in the germinal vesicles of amphibian oocytes. In the hnRNA population both complements of the repeats are found and can be readily detected because they form intermolecular duplex structures. The structure and formation of duplex regions have been studied in the hnRNA of Xenopus laevis, Triturus cristatus, Amphiuma means and Necturus maculosus, a series of amphibians of increasing genome size (C-value). In T. cristatus, the duplex structures are mostly 600-1200 bp in length, whereas in X. laevis they are shorter and in N. maculosus they tend to be longer. Although the proportion of RNA sequence capable of rapidly forming duplex structures is different in different organisms, this property bears no relationship to C-value. However the sequence complexity of complementary repeats, as estimated from the rate of duplex formation, does show an increasing trend with C-value. The complementary repeats found in oocyte hnRNA are transcribed from families of DNA sequence that are each represented in the genome by thousands of copies. The extent of cross-species hybridization is low, indicating that the repeat sequences transcribed in different amphibian genera are not the same. In situ hybridization experiments indicate that the repeat sequences are spread throughout the genome. The evolution and possible function of complementary repeats are considered.
重复序列在两栖类卵母细胞的生发泡中被转录。在核不均一RNA群体中，重复序列的两条互补链都能被找到，并且因为它们形成分子间双链结构而易于被检测到。已经对非洲爪蟾、有冠蝾螈、美洲鳗螈和黄斑美西螈（一系列基因组大小（C值）递增的两栖动物）的核不均一RNA中的双链区域的结构和形成进行了研究。在有冠蝾螈中，双链结构大多长度为600 - 1200碱基对，而在非洲爪蟾中它们较短，在黄斑美西螈中它们往往较长。尽管能够快速形成双链结构的RNA序列比例在不同生物体中有所不同，但这种特性与C值无关。然而，根据双链形成速率估算的互补重复序列的序列复杂性确实呈现出随C值增加的趋势。在卵母细胞核不均一RNA中发现的互补重复序列是从DNA序列家族转录而来的，这些家族中的每个序列在基因组中都有数千个拷贝。跨物种杂交的程度较低，这表明在不同两栖类属中转录的重复序列并不相同。原位杂交实验表明重复序列遍布整个基因组。文中还考虑了互补重复序列的进化及可能的功能。
