Kramerov D A, Tillib S V, Ryskov A P, Georgiev G P
Nucleic Acids Res. 1985 Sep 25;13(18):6423-37. doi: 10.1093/nar/13.18.6423.
Small poly(A)-containing RNA molecules which hybridize to the ubiquitous short repetitive sequence B2 and which are transcribed by RNA polymerase III have been identified in the cytoplasm of mouse cells. Here, we describe the structure of this small B2 RNA. A cDNA library was prepared from low-molecular-weight cytoplasmic poly(A)+RNA isolated from Ehrlich carcinoma cells and the clones which hybridized to B2 sequence were selected. The clones were sequenced and shown to contain B2 sequences followed by a poly(A) tract. The sequences of the cloned B2 RNAs different from each other by 3-10%, being similar in this respect to genomic B2 copies. Thus, B2 RNA is transcribed from many different B2 sequences in the genome. The 5'-ends of B2 RNA at least in most molecules coincide with the beginning of B2 genomic sequence. The poly(A) segments located at the 3'-end of small B2 RNA are the same size as in mRNA molecules, suggesting posttranscriptional formation. In some clones, additional sequences were detected between the 3'-end of B2 sequence and the poly(A) stretch. They seem to result from a lesion in the RNA polymerase III terminator in the corresponding B2 sequences. The possible significance of B2 sequences and small B2 RNA is discussed.
在小鼠细胞的细胞质中已鉴定出与普遍存在的短重复序列B2杂交且由RNA聚合酶III转录的含poly(A)的小RNA分子。在此，我们描述这种小B2 RNA的结构。从艾氏癌细胞中分离出的低分子量细胞质poly(A)+RNA制备了一个cDNA文库，并挑选出与B2序列杂交的克隆。对这些克隆进行测序，结果显示它们包含B2序列，后面跟着一个poly(A)尾。克隆的B2 RNA序列彼此之间相差3% - 10%，在这方面与基因组B2拷贝相似。因此，B2 RNA是从基因组中许多不同的B2序列转录而来的。至少在大多数分子中，B2 RNA的5'端与B2基因组序列的起始位置一致。位于小B2 RNA 3'端的poly(A)片段与mRNA分子中的大小相同，表明是转录后形成的。在一些克隆中，在B2序列的3'端和poly(A)片段之间检测到了额外的序列。它们似乎是由相应B2序列中RNA聚合酶III终止子的损伤导致的。本文还讨论了B2序列和小B2 RNA的可能意义。
