专题：Science报道
日美科学家在新一期美国《科学》杂志网络版上发表论文称，他们通过分析青鳉鱼脱氧核糖核酸（DNA）的全部信息，发现脱氧核糖核酸核小体（染色质的基本结构单位）结构影响着脱氧核糖核酸的变异，从而影响着生物进化。
东京大学日前发布新闻公报称，这一成果由东京大学和美国斯坦福大学科学家共同获得。
公报介绍说，多数科学家一直用达尔文的进化论和日本科学家木村资生的中性论这两套互相补充的理论来解释脱氧核糖核酸发生的变异。达尔文进化论的基本原理是，自然选择控制生物的进化，大自然将不断地淘汰不适宜生存的一切有害变异，只让有利变异生存下来。而木村资生在20世纪60年代提出，在分子水平上发生的基因变异是中性的，即对生物生存既无益也无害，自然选择对它不起作用。日本和美国科学家本次的新发现使人们对脱氧核糖核酸变异又有了新认识，这可能是反映脱氧核糖核酸变异新原理的基础性成果。
公报说，20世纪90年代后半期，有研究结果显示，脱氧核糖核酸核小体结构有可能影响脱氧核糖核酸的变异。科学家发现，在脱氧核糖核酸碱基修复试验中，脱氧核糖核酸核小体结构不同，碱基修复时间也存在显著差异。有科学家就猜测，在自然进化过程中，脱氧核糖核酸的变异或许会因核小体结构的不同而有差别，但科学家一直没有获得直接证据。
东京大学研究生院教授森下真一和美国斯坦福大学同行在本次研究中借助超高速脱氧核糖核酸解析装置，分析青鳉鱼所有脱氧核糖核酸核小体结构，结果证实了过去科学家的猜测。公报认为，这项研究成果可以部分说明生物遗传多样性的产生过程。
生物谷推荐原始出处：
Science DOI: 10.1126/science.1163183
Chromatin-Associated Periodicity in Genetic Variation Downstream of
Transcriptional Start Sites
Shin Sasaki 1, Cecilia C. Mello 2, Atsuko Shimada 3, Yoichiro Nakatani 1,
Shin-ichi Hashimoto 4, Masako Ogawa 4, Kouji Matsushima 4, Sam Guoping Gu
2, Masahiro Kasahara 1, Budrul Ahsan 1, Atsushi Sasaki 1, Taro Saito 1,
Yutaka Suzuki 5, Sumio Sugano 5, Yuji Kohara 6, Hiroyuki Takeda 3, Andrew
Fire 2*, Shinichi Morishita 7*
1 Department of Computational Biology, Graduate School of Frontier
Sciences, The University of Tokyo, Kashiwa 277–0882, Japan.
2 Departments of Pathology and Genetics, School of Medicine, Stanford
University, Stanford, CA 94305–5324, USA.
3 Department of Biological Sciences, Graduate School of Science, The
University of Tokyo, Tokyo 113–0033, Japan.
4 Department of Molecular Preventive Medicine, School of Medicine, The
University of Tokyo, Tokyo 113–0033, Japan.
5 Department of Medical Genome Sciences, Graduate School of Frontier
Sciences, The University of Tokyo, Tokyo 108–8639, Japan.
6 Center for Genetic Resource Information, National Institute of Genetics,
Mishima 411–8540, Japan.
7 Department of Computational Biology, Graduate School of Frontier
Sciences, The University of Tokyo, Kashiwa 277–0882, Japan.;
Bioinformatics Research and Development (BIRD), Japan Science and
Technology Agency (JST), Tokyo 102–8666, Japan.
Might DNA sequence variation reflect germline genetic activity and
underlying chromatin structure? Using two strains of medaka (Japanese
killifish, Oryzias latipes), we compared genomic sequence and mapped ~37.3
million nucleosome cores from medaka Hd-rR blastulae, together with 11,654
representative transcription start sites from six embryonic stages. We
observed a ~200–base pair (bp) periodic pattern of genetic variation
downstream of transcription start sites; the rate of insertions and
deletions longer than 1 bp peaked at positions of approximately +200,
+400, and +600 bp, whereas the point mutation rate showed corresponding
valleys. This ~200-bp periodicity was correlated with the chromatin
structure, with nucleosome occupancy minimized at positions 0, +200, +400,
and +600 bp. These data exemplify the potential for genetic activity
(transcription) and chromatin structure to contribute in molding the DNA
sequence on an evolutionary time scale.
