Jacob M, Lazar E, Haendler B, Gallinaro H, Krol A, Branlant C
Biol Cell. 1984;51(1):1-9. doi: 10.1111/j.1768-322x.1984.tb00278.x.
The four small nucleoplasmic RNAs designated as U1, U2, U4 and U5 RNA have a common structural domain or domain A. It is characterized by the presence of consensus sequence Pu-A-(U)5-G-Pup in a free single-stranded region and of the sequence Py-N-Py-Gp in the top loop of a hairpin located at the 3' end of the free region. Domain A is likely to be involved in a function common to the four small RNAs. Other domains possibly involved in the specific function of U1 and U5 RNAs are also presented. Several molecular forms of a same U RNA may be found in a same cellular type. These variant U RNAs are particularly numerous for U5 RNA. The possible origin of such new molecular forms is discussed in relation to multigene families for U RNAs. U1, U2, U4 and U5 RNAs are capped (with trimethylguanosine) and the consensus sequence for their 6 first nucleotides is A-(Py)5p. Thus, their 5' end resembles that of premessenger RNA, also capped (with monomethylguanosine) and bearing A-(Py)5p. Both classes of RNA are synthesized by RNA polymerase B, but the presence of a "TATA box" upstream of the capsite has not yet been demonstrated for U RNA genes. U1, U2, U4 and U5 RNAs bear a sequence C-Py-Pu at their 3' end or very close to it. This trinucleotide might be part of a site of post-transcriptional cleavage of U RNA precursors.(ABSTRACT TRUNCATED AT 250 WORDS)
四种被命名为U1、U2、U4和U5 RNA的小核仁RNA具有一个共同的结构域或结构域A。其特征在于在一个游离单链区域存在共有序列Pu-A-(U)5-G-Pup，以及在游离区域3'端发夹结构的顶部环中存在序列Py-N-Py-Gp。结构域A可能参与这四种小RNA的共同功能。文中还介绍了可能参与U1和U5 RNA特定功能的其他结构域。在同一细胞类型中可能会发现同一U RNA的几种分子形式。这些变体U RNA在U5 RNA中特别多。文中结合U RNA的多基因家族讨论了这种新分子形式的可能起源。U1、U2、U4和U5 RNA都有帽结构（三甲基鸟苷），其前6个核苷酸的共有序列是A-(Py)5p。因此，它们的5'端类似于前体信使RNA的5'端，也有帽结构（单甲基鸟苷）并带有A-(Py)5p。这两类RNA都是由RNA聚合酶B合成的，但对于U RNA基因，尚未证明在帽位点上游存在“TATA盒”。U1、U2、U4和U5 RNA在其3'端或非常靠近3'端处有一个序列C-Py-Pu。这个三核苷酸可能是U RNA前体转录后切割位点的一部分。（摘要截短于250字）
