IBMCP (CSIC-UPV), Valencia, Spain.
Adv Exp Med Biol. 2018;1087:53-63. doi: 10.1007/978-981-13-1426-1_5.
Circular DNAs are frequent genomic molecules, especially among the simplest life beings, whereas circular RNAs have been regarded as weird nucleic acids in biology. Now we know that eukaryotes are able to express circRNAs, mostly derived from backsplicing mechanisms, and playing different biological roles such as regulation of RNA splicing and transcription, among others. However, a second natural and highly efficient pathway for the expression in vivo of circRNAs has been recently reported, which allows the accumulation of abundant small (100-1000 nt) non-coding RNA circles through the participation of small self-cleaving RNAs or ribozymes called hammerhead ribozymes. These genome-encoded circRNAs with ribozymes seem to be a new family of small and nonautonomous retrotransposable elements of plants and animals (so-called retrozymes), which will offer functional clues to the biology and evolution of circular RNA molecules as well as new biotechnological tools in this emerging field.
环状 DNA 是常见的基因组分子，尤其是在最简单的生命形式中，而环状 RNA 则被认为是生物学中的奇怪核酸。现在我们知道，真核生物能够表达 circRNAs，这些 circRNAs 主要来源于反式剪接机制，并发挥不同的生物学作用，如 RNA 剪接和转录的调控等。然而，最近报道了 circRNAs 在体内表达的第二种自然而高效的途径，该途径通过参与称为锤头状核酶的小分子自我切割 RNA 或核酶，允许大量小（100-1000nt）非编码 RNA 环的积累。这些具有核酶的基因组编码的 circRNAs 似乎是动植物中一类新的小非自主逆转录转座元件（所谓的逆转酶），它们将为环状 RNA 分子的生物学和进化提供功能线索，并为这一新兴领域提供新的生物技术工具。
