约翰霍普金斯医学院的研究人员发现一种与众不同的microRNAs，这种microRNAs在其内部组件的带领下迁移到细胞核中。研究结果刊载于1月5日的Science中。
MicroRNAs在癌症和正常发育过程中，都发挥着重要的功能，microRNA可以附着、破坏携带蛋白编码序列的长链RNA，这也是MicroRNAs常出现在核糖体附近的原因。
Joshua Mendell率领的研究小组针对200多个已知的人类MicroRNAs进行分析调查时，发现一种与众不同的MicroRNA。
文章第一作者Hun-Way Hwang表示，这种MicroRNA出现的时间和出现的地点与预期的不同。MicroRNA通常由20－25个核苷酸构成，Mendell小组发现这种奇特的miR-29b末端的6个核苷酸序列，与其它 microRNA的末端明显不同，能够控制 microRNA在细胞中的定位。
研究人员将这六个核苷酸从miR-29b上剪切下来，连接到另一种microRNA上，结果新的microRNA与 miR-29b一样，会远离细胞蛋白质工厂而进入细胞核，将六个核苷酸连接在siRNA上，结果新的siRNA也会进入细胞核。
这些研究结果说明microRNAs虽然微小，但是其含有的短链核苷酸序列能够控制它们在细胞中的行为。Mendell希望利用在miR-29b中发现的细胞邮政编码，将其它microRNAs 和 siRNAs带入细胞核，以关闭特殊位置的基因。
由于microRNAs在癌症和正常的发育中有重要意义，所以研究人员希望针对miR-29b进一步研究，以发现microRNAs的更多功能。
英文原文：
Renegade RNA -- Clues to cancer and normal growth
Researchers at Johns Hopkins have discovered that a tiny piece of genetic code apparently goes where no bit of it has gone before, and it gets there under its own internal code.
A report on the renegade ribonucleic acid, and the code that directs its movement, will be published Jan. 5 in Science.
MicroRNAs, already implicated in cancer and normal development, latch on to and gum up larger strands of RNA that carry instructions for making the proteins that do all the cell's work. They are, says Joshua Mendell, M.D., Ph.D., an assistant professor in the McKusick-Nathans Institute of Genetic Medicine at Hopkins, like "molecular rheostats that fine-tune how much protein is being made from each gene."
That's why normally microRNAs always have appeared to stick close to the cell's protein-making machinery.
But during a survey of more than 200 of the 500 known microRNAs found in human cells, Mendell's team discovered one lone microRNA "miles away" --- in cellular terms --- from all the others.
"It was so clearly in the wrong place at the wrong time for what we thought it was supposed to be doing that we just had to figure out why," says Hun-Way Hwang, a graduate student in human genetics and contributor to the study.
Consisting of only 20 to 25 nucleotide building blocks (compared to other types of RNA that can be thousands of nucleotides long), each microRNA has a different combination of blocks. Mendell's team realized that six building blocks at the end of the wayward miR-29b microRNA were noticeably different from the ends of other microRNAs.
Suspicious that the six-block end might have something to do with miR-29b's location, the researchers chopped them off and stuck them on the end of another microRNA. When put into cells, the new microRNA behaved just like miR-29b, wandering far away from the cell's protein-making machinery and into the nucleus, where the cell's genetic material is kept.
The researchers then stuck the same six-block end onto another type of small RNA, a small-interfering RNA or siRNA that turns off genes. This also forced the siRNA into the nucleus.
According to Mendell, these results demonstrate for the first time that despite their tiny size, microRNAs contain elements consisting of short stretches of nucleotide building blocks that can control their behavior in a cell. Mendell hopes to take advantage of the built-in "cellular zip code" discovered in miR-29b as an experimental tool. For example, he plans to force other microRNAs and siRNAs into the nucleus to turn off specific sets of genes.
Mendell's team is actively hunting for additional hidden microRNA elements that control other aspects of their behavior in cells. They also are curious to figure out what miR-29b is doing in the nucleus. Because microRNAs have been implicated in cancer as well as normal development, Mendell hopes that further study of miR-29b will reveal other, hidden functions of microRNAs.
