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【bio-news】Science：分支转录起始机制
对大部分的基因来说与RNA聚合酶II相连的转录起始位点都被认为是单向性的。在本研究中，麻省理工等处的研究小组找出充足的证据证实编码蛋白的基因启动子区存在有分支转录的现象。转录起始位点与RNAs相连的区域（Transcription start site-associatied RNAs,TSSa-RNAs）非随机地从侧面激活启动子，在活性高峰期，反义与正义短RNAs各自位于TSSs（转录起始位点）的上游250个核苷酸的位置和TSSs下游50个核苷酸的位置。用Northern杂交技术分析显示，TSSa-RNAs是一类长度在20-90nt大小的RNA子群。启动子相关的RNA聚合酶II与H3K4-trimethylated histone以及转录起始标志（Transcription initiation hallmarks）都共同定位于正义和反义TSSs-RNA区；然而，H3K4-trimethylated histone延伸的特殊RNA聚合酶II只存在于TSSs的下游。
这些研究结果表明，启动子活性区域短距离内存在分支转录现象，这一现象可能有助于启动子区域维持平衡，确保次级调节活性。
Science 19 December 2008OI: 10.1126/science.1162253
Divergent Transcription from Active Promoters
Amy C. Seila,1* J. Mauro Calabrese,1,2* Stuart S. Levine,3 Gene W. Yeo,4 Peter B. Rahl,3 Ryan A. Flynn,1 Richard A. Young,2,3 Phillip A. Sharp1,2
Transcription initiation by RNA polymerase II (RNAPII) is thought to occur unidirectionally from most genes. Here, we present evidence of widespread divergent transcription at protein-encoding gene promoters. Transcription start site–associated RNAs (TSSa-RNAs) nonrandomly flank active promoters, with peaks of antisense and sense short RNAs at 250 nucleotides upstream and 50 nucleotides downstream of TSSs, respectively. Northern analysis shows that TSSa-RNAs are subsets of an RNA population 20 to 90 nucleotides in length. Promoter-associated RNAPII and H3K4-trimethylated histones, transcription initiation hallmarks, colocalize at sense and antisense TSSa-RNA positions; however, H3K79-dimethylated histones, characteristic of elongating RNAPII, are only present downstream of TSSs. These results suggest that divergent transcription over short distances is common for active promoters and may help promoter regions maintain a state poised for subsequent regulation.
1 Koch Institute, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
2 Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
3 Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, MA 02142, USA.
4 Salk Institute, Crick-Jacobs Center for Theoretical and Computational Biology, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA.hu
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作者:admin@医学,生命科学 2011-02-18 12:57
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