三疣梭子蟹基因组小卫星特征分析

Analysis of minisatellites in crab Portunus trituberculatus genome

通过构建三疣梭子蟹部分基因组文库，对获得的4164个克隆测序，共获得总长度h622409bp的DNA序列。在序列拼接后长度500--1500bp的709个克隆中，筛选到130个小卫星序列，其序列总长度占测序序列总长度的2．55％。小卫星序列中，以12bp重复单位的序列数量最多（10．77％），总体趋势表现为重复单位越长，相应的重复序列数目越少（R=-0．663，P〈0．01）。小卫星重复单位拷贝数分布范围以8bp重复单位最广为3．9～66．5；其次是13bp重复范围在2．0～40．6；再次是26bp重复，范围在2．3～21．0。平均拷贝数最高的三种重复类型分别为8bp重复（19．96），25bp重复（16．00）和22bp重复（15．85）。小卫星序列中各重复单位的拷贝数分布范围2～66．5，集中分布在2～25，且表现为拷贝数目越大，其相应的重复序列数目越低的趋势。130个重复序列分别由123种重复单位所组成，因而小卫星重复序列的类型很多。初步分成三类：2种碱基组成类别、3种碱基组成类别和4种碱基组成类别，并进一步根据各个重复序列中所含有的碱基种类的数量从大到小排列这些碱基而分成若干小类。从这些分类中可以看出，三疣梭子蟹基因组中的小卫星整体上是富含A／T的重复序列，并揭示了其与微卫星重复序列之间的关系，即一部分小卫星重复序列可能起源于微卫星序列。

In this paper, genome library of crab Portunus trituberculatus was constructed. By sequencing randomly, 4 164 clones of sequences in the genomic library of crab Portunus trituberculatus were obtained. Then, using software DNASTAR （Version 5.0） to assemble all of the clones, 709 clones independent of each other, were made in which the length of DNA sequences is about 622 409 bp in total. With the help of the bio-soh Tandem Repeats Finder （Version 2.02）, 130 minisatellites were screened in the crab＇s genome DNA sequences. Their cumulative length occupied 2.55% of the total length of DNA sequences. In the minisatellite sequences, twelve-nucleotide repeats were the most frequent type, accounting for 10.77% of the total number of minisatellites. It showed that the number of sequences decreased with the length of its repeat unit（R = -0. 663, P〈0.01）. Eight-nucleotide repeat had the largest range of copy number of repeat unit （3.9 - 66.5）, the following were thirteen-nucleotide repeat type（2.0 - 40.6） and twenty-six-nucleotide（2.3 - 21.0）, respectively. Descending three repeat types in mean copy number of repeat unit were eight-nucleotide repeat （19.96）, twenty-five-nucleotide （16.00）and twenty-two-nucleotide （15.85）, respectively. The range of copy number of repeat unit varied from 2 to 66.5, and the copy number mostly ranged from 2 to 25. Moreover, it was showed that the number of corresponding minisatellites decreased as copy number of repeat unit increased. In this research, the 130 minisatellite sequences are composed of 123 kinds of repeat units, so it is very difficult to classify the minisatellite sequences. The minisatellite sequences can be classified into three types： dinucleotide minisatellite sequences composed of two kinds of nucleotide, trinucleotide minisatellite sequences composed of three kinds of nucleotide and tetranucleotide minisatellite sequences composed of four kinds of nucleotide. Further, all of above sequences can be divided into many sub-types according to the composition of nucleotide and their number from large to small. Totally, the minisatellite sequences in Portunus trituberculatus are A/T rich. This paper also discussed the genesis and evolution of minisatellite repeat sequences, and it is belived that the minisatellite repeats may come from the microsatellite repeats. It could be very practical to use minisatellite to study the genome of Portunus trituberculatus and would be applied to a variety of fields.