Riccardo Sara, Tortoriello Giuseppe, Giordano Ennio, Turano Mimmo, Furia Maria
Department of Structural and Functional Biology, University of Naples Federico II, Complesso Universitario Monte Santangelo via Cinthia, Napoli, Italy.
BMC Mol Biol. 2007 Feb 28;8:15. doi: 10.1186/1471-2199-8-15.
In eukaryotic cells, each molecule of H/ACA small nucleolar RNA (snoRNA) assembles with four evolutionarily conserved core proteins to compose a specific ribonucleoprotein particle. One of the four core components has pseudouridine synthase activity and catalyzes the conversion of a selected uridine to pseudouridine. Members of the pseudouridine synthase family are highly conserved. In addition to catalyzing pseudouridylation of target RNAs, they carry out a variety of essential functions related to ribosome biogenesis and, in mammals, to telomere maintenance. To investigate further the molecular mechanisms underlying the expression of pseudouridine synthase genes, we analyzed the transcriptional activity of the Drosophila member of this family in great detail.
The Drosophila gene for pseudouridine synthase, minifly/Nop60b (mfl), encodes two novel mRNAs ending at a downstream poly(A) site. One species is characterized only by an extended 3'-untranslated region (3'UTR), while a minor mRNA encodes a variant protein that represents the first example of an alternative subform described for any member of the family to date. The rare spliced variant is detected mainly in females and is predicted to have distinct functional properties. We also report that a cluster comprising four isoforms of a C/D box snoRNA and two highly related copies of a small ncRNA gene of unknown function is intron-encoded at the gene-variable 3'UTRs. Because this arrangement, the alternative 3' ends allow mfl not only to produce two distinct protein subforms, but also to release different ncRNAs. Intriguingly, accumulation of all these intron-encoded RNAs was found to be sex-biased and quantitatively modulated throughout development and, within the ovaries, the ncRNAs of unknown function were found not ubiquitously expressed.
Our results expand the repertoire of coding/non-coding transcripts derived from the gene encoding Drosophila pseudouridine synthase. This gene exhibits a complex and interlaced organization, and its genetic information may be expressed as different protein subforms and/or ncRNAs that may potentially contribute to its biological functions.
在真核细胞中，每个H/ACA小核仁RNA（snoRNA）分子与四种进化上保守的核心蛋白组装在一起，构成一个特定的核糖核蛋白颗粒。这四种核心成分之一具有假尿苷合酶活性，并催化选定的尿苷转化为假尿苷。假尿苷合酶家族成员高度保守。除了催化靶RNA的假尿苷化外，它们还执行多种与核糖体生物发生相关的基本功能，在哺乳动物中还与端粒维持有关。为了进一步研究假尿苷合酶基因表达的分子机制，我们详细分析了该家族果蝇成员的转录活性。
果蝇假尿苷合酶基因minifly/Nop60b（mfl）编码两种新的mRNA，其末端位于下游的多聚腺苷酸化位点。一种类型仅以延长的3'-非翻译区（3'UTR）为特征，而一种次要的mRNA编码一种变体蛋白，这是该家族迄今为止任何成员中描述的替代亚型的第一个例子。这种罕见的剪接变体主要在雌性中检测到，预计具有不同的功能特性。我们还报告说，一个由C/D盒snoRNA的四种同工型和一个功能未知的小ncRNA基因的两个高度相关拷贝组成的簇在内含子编码于基因可变的3'UTR处。由于这种排列，可变的3'末端使mfl不仅能够产生两种不同的蛋白质亚型，还能释放不同的ncRNA。有趣的是，发现所有这些内含子编码的RNA的积累存在性别偏向，并且在整个发育过程中受到定量调节，在卵巢中，功能未知的ncRNA并非普遍表达。
我们的结果扩展了源自果蝇假尿苷合酶编码基因的编码/非编码转录本的种类。该基因表现出复杂且交错的组织形式，其遗传信息可能以不同的蛋白质亚型和/或ncRNA的形式表达，这可能潜在地有助于其生物学功能。
