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【bio-news】科学家发现＂Dueling RNAs＂功能
11/16/06 -- Researchers have found that a class of RNA molecules, previously thought to have no function, may in fact protect sex cells from self-destructing. These findings will be published in the November 17 issue of the journal Cell.
Central to this discovery is the fundamental process of gene expression. When a gene is ready to produce a protein, the two strands of DNA that comprise the gene unravel. The first strand produces a molecule called messenger RNA, which acts as the protein's template. Biologists call this first strand of DNA the "sense" or "coding" transcript. Even though the other strand doesn't contain a protein recipe, it may also, on occasion, produce an "anti-sense" RNA molecule, one whose sequence is complementary to that of the messenger, or sense, RNA. Antisense RNA has been detected for a number of genes, but is largely considered a genetic oddity.
Using common baker's yeast, Cintia Hongay, a postdoctoral researcher in the lab of Whitehead Member and MIT Professor Gerald Fink, discovered that in the case of a gene called IME4, the antisense RNA blocks the sense RNA. In other words, the gene disables its own ability to make protein.
"This is the first case where a specific function in a higher cell for antisense RNA has been found," says Fink, senior author on the paper. "This points to an entirely new process of gene regulation that we've never seen before in eukaryotic cells."
There is a method to this sense/antisense madness, one that has a kind of yin and yang quality. When conditions around yeast cells are good and rich in nutrients, the cells divide by mitosis--that is, the DNA duplicates so each daughter cell receives exactly the same number of chromosomes as the original cell. However, when the yeast cells are starving, IME4 switches on and activates a process called meiosis. Here, the cells divide into germ-cell spores that, like mammalian egg and sperm cells, have half the number of chromosomes. Yeast spores withstand this harsh environment far more ably than the larger cells from which they originate.
But in some cases, flipping the meiotic switch can be catastrophic. If a cell with only one copy of each chromosome (a haploid cell) is forced into meiosis, the progeny won't survive. Fortunately, such destructive meiotic division is avoided in haploid cells because they continually produce IME4 antisense RNA, blocking the production of sense RNA. Antisense IME4, then, safeguards against meiosis in cells that can't handle it.
"This is the first time that we've found a function for antisense RNA, that is not RNAi, in a higher cell type," says Hongay. "In fact, it's really the first time we've seen a gene regulate itself in this way."
"For years scientists have evaluated genomes by measuring the sense RNA, with antisense transcripts thought to have no meaning at all," says Fink. "Here we've found a process in which antisense RNA regulates sense RNA. This same process may occur in the sex cells of mammals. In fact, considering how widespread these antisense transcripts are, I wouldn't be surprised if these findings eventually lead us to discover an entirely new level of gene regulation."
Hongay is now searching the yeast genome for other genes that might be regulated by antisense RNA.
Source: Whitehead Institute for Biomedical Research
http://www.bio.com/newsfeatures/newsfeatures_research.jhtml;jsessionid=4TCBX43SK3RJ5R3FQLMSFEWHUWBNQIV0?cid=23900002 我认领这个，超过48小时没搞定，麻烦朋友些帮忙 周末下午没事，速度交稿，积累人品。。
科学家发现“相扑”RNA
11/16/06 研究人员最近发现，一种以前认为没有功能的RNA分子，可能在自我调控过程中起到保护 性细胞的作用。这项研究发现将发表在11月份的CELL第17期。
这项研究的中心是基因表达的基本途径。当基因表达蛋白质，基因的双链DNA将解旋。第一条链生成信使RNA，信使RNA是作为蛋白表达的模板。生物学家一般称第一条DNA链为“正义”/“编码”序列。尽管另一条链没有包含蛋白质编码，但是却有可能生成“反义”RNA，“反义”RNA的序列与信使/“正义”RNA序列互补。反义RNA已经在很多基因中发现，但是大部分还是只被当作一种遗传变异。
白头生物中心的博士后Cintia Hongay和麻绳理工的Gerald Fink利用普通酵母菌进行研究，发现在IME4基因存在的情况下，反义RNA将阻断编码RNA的作用。换句话说，这时基因失去了表达蛋白的能力。
论文主要作者Fink如是说到：“这是首次在高级细胞中发现反义RNA的特殊作用，在以前的真核细胞中是没有观察到的，这项研究为基因规则提供了一条全新的路径。”
可以用阴、阳来概括编码和反义RNA的机制。当酵母细胞生长环境优良、营养充足时，细胞进行有丝分裂，DNA复制后，每个子代细胞与原代细胞含有相同数目的染色提。而当酵母生长环境恶劣时，IME4表达开启并激活减数分裂途径。减数分裂中，细胞分裂成孢子，类似哺乳动物的卵子和精子，豹子内只有一半数目的染色体。孢子在恶劣环境下的生存力大大优于他们的“父辈”。
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作者:admin@医学,生命科学 2011-05-22 19:00
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