Nucleotide sequence of cloned unintegrated avian sarcoma virus DNA: viral DNA contains direct and inverted repeats similar to those in transposable elements.
Nucleotide sequence of cloned unintegrated avian sarcoma virus DNA: viral DNA contains direct and inverted repeats similar to those in transposable elements.
复制标题
克隆的未整合禽肉瘤病毒DNA的核苷酸序列：病毒DNA含有与转座元件类似的直接和反向重复序列。
DOI：
10.1073/pnas.78.1.124
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发表时间：
1981
影响因子：
11.1
通讯作者：
Varmus,HE
中科院分区：
文献类型：
--
作者：
Swanstrom,R;DeLorbe,WJ;Bishop,JM;Varmus,HE
我们测定了在原核宿主-载体系统中克隆的两个环状禽肉瘤病毒（ASV）DNA分子的部分核苷酸序列。其序列被确定的区域代表环连接位点--即，未整合的线性DNA末端融合形成环状DNA的位点。来自一个克隆分子SRA-2的序列显示，环状连接位点是330个碱基对（bp）串联直接重复的中心，推测代表已知存在于线性DNA末端的长末端重复（LTR）单位的融合。环连接位点也是15 bp不完全反向重复的中心，因此出现在LTR的边界。ASV DNA的结构--独特的编码区两侧是一个直接重复序列，反过来又以一个短的反向重复序列终止--与某些转座因子的结构非常相似。序列的几个特征意味着形成SRA-2分子的环化发生而没有损失来自线性DNA前体的信息。另一个克隆的病毒DNA分子SRA-1的环化可能是通过不同的机制发生的。SRA-1分子的环连接位点有一个63 bp的缺失，这可能是由类似于病毒DNA整合到宿主基因组中的机制引起的。串联同向重复序列的一侧是tRNATrp的结合位点，tRNATrp是先前描述的用于合成病毒DNA第一链的引物。同向重复序列的另一侧侧接多嘌呤段A-G-G-G-A-G-G-G-G-G-A，其可代表用于合成病毒DNA第二链的引物的位置。RNA加帽位点上游的富含A+ T的区域和序列A-A-T-A-A-A存在于同向重复序列内。这些序列可以分别作为启动子位点和poly（A）添加信号，如针对其他真核转录单位所提出的。
We have determined the nucleotide sequence of portions of two circular avian sarcoma virus (ASV) DNA molecules cloned in a prokaryotic host--vector system. The region whose sequence was determined represents the circle junction site--i.e., the site at which the ends of the unintegrated linear DNA are fused to form circular DNA. The sequence from one cloned molecule, SRA-2, shows that the circle junction site is the center of a 330-base-pair (bp) tandem direct repeat, presumably representing the fusion of the long terminal repeat (LTR) units known to be present at the ends of the linear DNA. The circle junction site is also the center of a 15-bp imperfect inverted repeat, which thus appears at the boundaries of the LTR. The structure of ASV DNA--unique coding region flanked by a direct repeat that is, in turn, terminated with a short inverted repeat--is very similar to the structure of certain transposable elements. Several features of the sequence imply that circularization to form the SRA-2 molecule occurred without loss of information from the linear DNA precursor. Circularization of another cloned viral DNA molecule, SRA-1, probably occurred by a different mechanism. The circle junction site of the SRA-1 molecule has a 63-bp deletion, which may have arisen by a mechanism that is analogous to the integration of viral DNA into the host genome. Flanking one side of the tandem direct repeat is the binding site for tRNATrp, the previously described primer for synthesis of the first strand of viral DNA. The other side of the direct repeat is flanked by a polypurine tract, A-G-G-G-A-G-G-G-G-G-A, which may represent the position of the primer for synthesis of the second strand of viral DNA. An A+T-rich region, upstream from the RNA capping site, and the sequence A-A-T-A-A-A are present within the direct repeat sequence. These sequences may serve as a promoter site and poly(A) addition signal, respectively, as proposed for other eukaryotic transcription units.