The molluscan 28S ribosomal RNA (rRNA) naturally cleaves into two fragments of similar size as 18S rRNA. This phenomenon, known as the hidden break, has been described in many other protostome species. Here, we characterize the 28S rRNA hidden break region in seven giant clam species, Tridacna gigas, T. derasa, T. maxima, T. noae, T. crocea, Hippopus hippopus and H. porcellanus. We confirm that the break consistently occurs in giant clams and is observed in all tissues and developmental stages. The region of the giant clam 28S rRNA break is located at a position homologous to the well-characterized 28S rRNA break in insects. High AU content and a stem–loop secondary structure in the region may contribute to fragmentation of the 28S rRNA molecule. An awareness of the existence of the hidden break in molluscs, such as the giant clams, which are emerging systems for understanding how environmental change affects life in the ocean, will facilitate progress of RNA sequencing-based analyses that currently rely on standard RNA profiles as a measure of sample integrity.

中文翻译：

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巨蛤28S核糖体RNA隐藏断裂的表征

软体动物 28S 核糖体 RNA (rRNA) 自然切割成两个与 18S rRNA 大小相似的片段。这种被称为隐藏断裂的现象已在许多其他原虫物种中得到描述。在这里，我们描述了七种巨型蛤蜊，Tridacna gigas，T.derasa，T. maxima，T. noae，T. crocea，Hippopus hippopus 和 H. porcellanus 的 28S rRNA 隐藏断裂区域。我们确认这种断裂始终发生在巨型蛤蜊中，并且在所有组织和发育阶段都可以观察到。巨蛤 28S rRNA 断裂区域位于与昆虫中充分表征的 28S rRNA 断裂同源的位置。该区域的高 AU 含量和茎环二级结构可能有助于 28S rRNA 分子的片段化。意识到软体动物中存在隐藏的裂缝，例如巨型蛤蜊，