Chang D Y, Hsu K, Maraia R J
Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
Nucleic Acids Res. 1996 Nov 1;24(21):4165-70. doi: 10.1093/nar/24.21.4165.
Nearly 1 000 000 copies of Alu interspersed elements comprise approximately 5% of human DNA. Alu elements cause gene disruptions by a process known as retrotransposition, in which dimeric Alu RNA is a presumed intermediate. Dimeric Alu transcripts are labile, giving rise to stable left monomeric scAlu RNAs whose levels are tightly regulated. Induction of Alu RNA by viral infection or cell stress leads to a dramatic increase in dimeric Alu transcripts, while scAlu RNA increases modestly. Each monomer of the dimeric Alu element shares sequence homology with the 7SL RNA component of the signal recognition particle (SRP). The SRP protein known as SRP9/14 is also found in a discrete complex with scAlu RNA, although whether dimeric Alu RNA is associated with SRP9/14 had been unknown. Here we show that antiserum to human SRP9 immunoprecipitates both scAlu RNA and dimeric Alu RNAs and that these RNPs accumulate after adenovirus infection, while levels of SRP9, SRP14, SRP54 and 7SL SRP RNA are unaffected. Dimeric Alu RNAs are also associated with the La protein, indicating that these are indeed nascent RNA polymerase III transcripts. This report documents that induced Alu transcripts are assembled into SRP9/14-containing RNPs in vivo while SRP levels are unchanged. Implications for Alu RNA metabolism and evolution are discussed.
近100万个Alu散布元件约占人类DNA的5%。Alu元件通过一种称为逆转座的过程导致基因破坏，在这个过程中，二聚体Alu RNA被认为是中间产物。二聚体Alu转录本不稳定，会产生稳定的左单体scAlu RNA，其水平受到严格调控。病毒感染或细胞应激诱导Alu RNA会导致二聚体Alu转录本急剧增加，而scAlu RNA适度增加。二聚体Alu元件的每个单体与信号识别颗粒（SRP）的7SL RNA成分具有序列同源性。名为SRP9/14的SRP蛋白也存在于与scAlu RNA形成的离散复合物中，尽管二聚体Alu RNA是否与SRP9/14相关尚不清楚。在这里，我们表明抗人SRP9抗血清能免疫沉淀scAlu RNA和二聚体Alu RNA，并且这些核糖核蛋白在腺病毒感染后积累，而SRP9、SRP14、SRP54和7SL SRP RNA的水平不受影响。二聚体Alu RNA也与La蛋白相关，表明它们确实是新生的RNA聚合酶III转录本。本报告证明，诱导的Alu转录本在体内组装成含有SRP9/14的核糖核蛋白，而SRP水平不变。文中讨论了其对Alu RNA代谢和进化的影响。
